Great build, you really scored on that one with a nice collection of parts.
The brakes look to be random brand, cant tell. Disassemble amd clean them up make sure theres no binding or worn parts in the pivot.
Brake pads - scuff them off woth a file to get fresh material to the surface. Set your pads as close to the rim as possible without rub, you want the backside of the pad as it passes thru the wheel to hit first and be sure the face of the pad is lined up square to the rim. New cable will help too, a lot is just adjusting.
Make sure the release evenly, may need to bend the spring out to get some tension back in it, one or both sides.