If you have more then one ship with the same PS, can you see the range of all before you choose which attacks first?

I've heard two different answers that both people backed up with the rule book...one argued there is only one "active ship" at a time, so you can't. Another showed that you can view range before deciding who can attack, and interpreted that as the active ship doesn't need to attack at that time (or some logic like that).

Which is right?

You can choose the order of attack, but since you can not measure befor begining your attack (step 1 of attack is to declare target and this is where you measure, see Declare target at p10 of the core rule book) you can not measure from any other ship then the one you select to attack with.

Or to put it short, you can not measure any ranges befor selecting which ship will attack next.

This issue tends to come up because there are kinda two sets of rules for Xwing. The rules that come with the rulebook, and then the more restrictive set of rules that are laid out in the Competitive Play section of the FAQ. To answer directly your question:

From the FAQ, Page 6, Competitive Play, Measuring Range section:

Measuring Range Players may only measure range and/or use the range ruler to determine whether a ship is inside or outside of a firing arc at the following times:

• When a ship becomes the active ship during the combat phase, the active player can measure range from the active ship to any enemy ships before declaring one as its target

• When a player declares a ship’s ability that requires another ship (or ships) to be at a certain range, the player trying to resolve the ability can measure range from their ship to any valid ships before resolving the ability.

• After declaring the intended target of a target lock action, the active player may measure range to the intended target, and only to the intended target.

The first bullet point above directly relates to your question. Under the Competitive Play rules, once you declare a ship as the attacker, only that ship can measure firing ranges until after it has taken it's shot. After that ship's shot is completed, another ship is chosen as the attacker, and it takes it's shot.

The Core rule book is just more relaxed, while the Competitive play FAQ section is more restricted. Most games are played with the Competitive Play section of the FAQ in effect, but that's up to you and your opponent, unless of course this is a tournament.

This one isn't actually Core vs. Competitive issue. The rulebook tells you when you can measure something. In this case, you can measure before declaring a target, which is in Step 1, after you've declared the active ship. The Competitive rules lay it out in somewhat greater detail, but it's not actually any different.