I have been asked to co sign for an apartment for my brother and uncle to move into. My uncle has bad credit and now they need me to co sign for the 1year lease. Im wondering if could I make up a contract for my brother and uncle to sign to pay me back if they break the lease. Would that hold up in a court of law.

Of course you can but you would have the same luck getting your money as the landlord was having,

Do the what if's. If they move out in 6 months, do 2000 in damage moving out, are you ready to pay them 3 or 4 thousand dollars?
If they can't afford to rent, let them find somewhere they can get into on their own. Do not co-sign for them.
It is only going to hurt your credit. When they get evicted and you get sued, ( without notice they are getting evicted) that judgement will be on your credit record, just like it was yours.

I agree 100% with Fr Chuck.

Do NOT co-sign.

If they can't afford this place, let them find another place they CAN afford.