Do the attacks from two weapon weilder (melee) stack with the extra attacks from swift attack? if they don't, then what is the point of having two melee weapons?

They do stack. So if you're using a weapon in each hand, the main hand gets the benefits of Swift Attack and /or Lightning Attack, while the offhand weapon makes one attack only by virtue of the Dual Weapon Wielder. So with either of the multiple attack talents and dial you add one attack.

The errata thoroughly describes the interactions of most of the combat talents, and can be found here.