A Thri Kreen has multiple limbs according to page 15 of the expanded psionics handbook:
Multiple Limbs thri-kreen have four arms and thus can take the Multiweapon Fighting feat page 304 of the Monster Manual instead of the Two-Weapon Fighting feat. Thri-kreen can also take the Multiattack feat these feats are not bonus feats.
The multiweapon fighting feat is described thus:
Multiweapon Fighting penalties for fighting with multiple weapons are reduced by 2 with the primary hand and reduced by 6 with off hands. Normally a creature without this feat takes a -6 penalty on attacks made with its primary hand and a -10 penalty on attacks made with its off hands. It has one primary hand and all the others are off hands.
If a thri-kreen uses two long swords in a two handed grip what happens? According to page 134 of the player's handbook, we can see:
Strength Bonus: When you hit with a melee or thrown weapon, including a sling, add your Strength modifier to the damage result. A Strength penalty, but not a bonus, applies on attacks made with a bow that is not a composite bow.
Off-Hand Weapon: When you deal damage with a weapon in your off hand, you add only 1/2 your Strength bonus.
Wielding a Weapon Two-Handed: When you deal damage with a weapon that you are wielding two-handed, you add 1-1/2 times your Strength bonus. However, you don’t get this higher Strength bonus when using a light weapon with two hands (see Light, One-Handed, and Two-Handed Melee Weapons, page 113).
So the question is, on the off hand long sword wielded two handedly does the thri-kreen add only half his strength bonus with the off hand long sword or does he add 1-1/2 times his strength bonus or does he add 0.75 his strength bonus, or some other calculation?