I just mc my lvl 4 fighter to a lvl 2 sorcerer and my lvl 5 thief to a lvl 1 wiz but I cant cast spells with them.

I chose a couple of spells for the fighter and made a button on my task bar and I can see the spells there but they are greyed out and unclickable. When I look on the spell page the spells are there and I should have 3 available.

As for the thief I memorised some scrolls but can't select any spells to memorise.

What's up??

"I just mc my lvl 4 fighter to a lvl 2 sorcerer and my lvl 5 thief to a lvl 1 wiz but I cant cast spells with them."

Probably their stats don't allow them to cast spells. For a Sorcerer, you need a Cha score of 10 + the level of the spell to cast it; for a Wizard, you need an Int score of 10 + the level of the spell. So if the fighter/sorc doesn't have an 11 Cha, and the rogue/wiz doesn't have an 11 Int, that would explain it.

Is there any items that lessesns the spellcasting ability?

I don't think any items will outright prevent you from casting spells. But if you're casting Arcane spells, then armor and shields will sometimes cause spell failures (right click the armor/shield in question to see how high a % chance of arcane spell failure they bring with them). The armored arcana feats can reduce that % chance, but IMHO it's not really worth it, just don't use armor or shields with an arcane caster (or at most, only use a small shield and take one rank of AA).