Diagnosing the squeaking problem and the solution to your understeer problem both involve one thing. Remove the Hotchkis rear sway bar. If the squeak goes away without the bar, there is the problem. To correct the understeer caused by the stiff (in roll) front end, you can add a bigger rear sway bar which will involve removing the Hotchkis bar as well.

Solid, sway bar torsional stiffness is a function of diameter^4. In comparing torsional stiffness, the Progress, Whiteline or TRD rear sways are all darn near 10 times as stiff as the rear Hotchkis sway. This will help put the two front wheels back on the ground.