I am looking at all possible stacking of co-pilot upgrades with ships with more than one slot (lambda shuttle, yt-1300 and now the cr-90). I am curious if it possible to take two weapons engineers and have their effects stack, so getting to maintain 4 target locks.

They don't stack, the verbiage is specific to maintaining 2 target locks, not an additional one.

Well I would agree with that. However, in the FAQ they give the example of stacking two mercenary co-pilots and on their cards there is not mention of words “additional.”

Yes, sadly, Weapon's Engineer doesn't stack. Mercenary Co-Pilots do stack. To see why, let's look at the wording:

In Weapon's Engineer, it specifically says you may HAVE TWO target locks on two ships and my acquire TWO TLs when acquiring one. That doesn't really stack.

With Merc Copilot, it says you may change one hit to a crit. However, this verbiage does not preclude changing another hit to a crit. Since you may only use a card once per opportunity (Merc Copilot can't change them all to crits and Luke can't change all eyes to evades), but you may use multiple cards on the same opportunity, this means we can change two hits to crits.

I do generally agree with that, it just seemed like a bit of the rules that are a little hazy. I suppose you could also make the argument that because mercenary copilot gives a unique ability that not normally achievable (compared to an action, like target locking or something similar) that it does not need the word additional to stack the abilities. It’s a shame because I would really like to flying around with 4 targets locks every turn and Han Solo in my Tantive IV

Currently existing and/or spoilered crew that can double-stack. Note that these can potentially Triple or Quadruple stack on Huge Ships.

• Intelligence Agent
  Look at the dials of up to Two enemy ships at Range 1-2
• Mercenary Co-Pilot
  Turn up to 2 [boom]s into [KABLAM]s when attacking at Range 3
• Tactician
  Deal 2 stress tokens when attacking in your arc at Range 2
• Reconnaissance Specialist
  Gain 2 extra Focus Tokens when performing a Focus action, for a net total of 3.
• Targeting Coordinator
  You may spend up to 2 Energy to acquire Target Locks for up to 2 friendly ships at Range 1-2
• Flight Instructor
  You may re-roll up to 2 [Eye]s while defending, or up to 2 [___]s if the attacker's PS is 2 or lower.
  

Currently existing and/or spoilered crew that can double-stack. Note that these can potentially Triple or Quadruple stack on Huge Ships.

• Intelligence Agent

  Look at the dials of up to Two enemy ships at Range 1-2

• Mercenary Co-Pilot

  Turn up to 2 [boom]s into [KABLAM]s when attacking at Range 3

• Tactician

  Deal 2 stress tokens when attacking in your arc at Range 2

• Reconnaissance Specialist

  Gain 2 extra Focus Tokens when performing a Focus action, for a net total of 3.

• Targeting Coordinator

  You may spend up to 2 Energy to acquire Target Locks for up to 2 friendly ships at Range 1-2

• Flight Instructor

  You may re-roll up to 2 [Eye]s while defending, or up to 2 [___]s if the attacker's PS is 2 or lower.

You can’t take two Reconnaissance Specialist because the card says limited, but I would agree with all the others.

Also, I don't how you could quadruple even on a large ship. The max copilots is 3 with the Tantive IV title.

Currently existing and/or spoilered crew that can double-stack. Note that these can potentially Triple or Quadruple stack on Huge Ships.

• Intelligence Agent

  Look at the dials of up to Two enemy ships at Range 1-2

• Mercenary Co-Pilot

  Turn up to 2 [boom]s into [KABLAM]s when attacking at Range 3

• Tactician

  Deal 2 stress tokens when attacking in your arc at Range 2

• Reconnaissance Specialist

  Gain 2 extra Focus Tokens when performing a Focus action, for a net total of 3.

• Targeting Coordinator

  You may spend up to 2 Energy to acquire Target Locks for up to 2 friendly ships at Range 1-2

• Flight Instructor

  You may re-roll up to 2 [Eye]s while defending, or up to 2 [___]s if the attacker's PS is 2 or lower.

You can’t take two Reconnaissance Specialist because the card says limited, but I would agree with all the others.

Also, I don't how you could quadruple even on a large ship. The max copilots is 3 with the Tantive IV title.

Recon Specialist was printed before "Limited" was a thing. I just spelled out the full word.

Moreover, I am fairly certain that "Limited" only appears on Team upgrades, not Crew.

Tantive IV lets you take 3 in the Fore and 1 in the Aft, and all 4 effect your ship.

Currently existing and/or spoilered crew that can double-stack. Note that these can potentially Triple or Quadruple stack on Huge Ships.

• Intelligence Agent

  Look at the dials of up to Two enemy ships at Range 1-2

• Mercenary Co-Pilot

  Turn up to 2 [boom]s into [KABLAM]s when attacking at Range 3

• Tactician

  Deal 2 stress tokens when attacking in your arc at Range 2

• Reconnaissance Specialist

  Gain 2 extra Focus Tokens when performing a Focus action, for a net total of 3.

• Targeting Coordinator

  You may spend up to 2 Energy to acquire Target Locks for up to 2 friendly ships at Range 1-2

• Flight Instructor

  You may re-roll up to 2 [Eye]s while defending, or up to 2 [___]s if the attacker's PS is 2 or lower.

You can’t take two Reconnaissance Specialist because the card says limited, but I would agree with all the others.

Also, I don't how you could quadruple even on a large ship. The max copilots is 3 with the Tantive IV title.

Recon Specialist was printed before "Limited" was a thing. I just spelled out the full word.

Moreover, I am fairly certain that "Limited" only appears on Team upgrades, not Crew.

Tantive IV lets you take 3 in the Fore and 1 in the Aft, and all 4 effect your ship.

Sorry I meant to say targeting coordinator not recon specialist

The base CR90 has one copilot in the fore and one in the aft, and the tantive IV title gives your +1 to your fore. For a total of 3. However you do get up to 4 "teams" with the tantive IV title, which doesn't make a lot of sense because there are only 3 team cards (so far).

I do generally agree with that, it just seemed like a bit of the rules that are a little hazy. I suppose you could also make the argument that because mercenary copilot gives a unique ability that not normally achievable (compared to an action, like target locking or something similar) that it does not need the word additional to stack the abilities. It’s a shame because I would really like to flying around with 4 targets locks every turn and Han Solo in my Tantive IV

The rules really are not that hazy, there is a very specific differentiation of the wording used.

Here is the run down to try and clarify:

You have 2 weapons engineers, and you go to acquire a TL. WE #1 triggers and changes the rules of TLing to allow you to acquire 2 TLs. WE #2 triggers and changes the rules of TLing to allow you to acquire 2 TLs. After both have triggered, you are allowed to acquire 2 TLs. The second one is redundant.

You have 2 Merc copilots and are firing at range 3. You roll 3 hits, MC #1 triggers and changes 1 hit to crit. You now have 1 crit, 2 hits. MC #2 triggers and changes a hit to a crit. You now have 2 crits and 1 hit. The second one was not redundant.