Are they bolts? Not unheard of but fairly unusual. If bolts use a flat ended punch and a small hammer. With the punch on the bolt head and using light, rapid blows with the hammer. If steel nuts and studs, forget what size they should be, instead use a spanner that can be persuaded to fit, even if you need to tap it on. I don't usually abuse tools but this is an exception.
If time permits, build small "cups " under each stud/bolt, these can be out of blue tack or plasticine and then fill these with penetrating fluid. Think Swallows nests......
To clarify, the punch method isn't to undo the bolt, it's to shock the threads, so used on the bolt head, axially.