Duck, I don't even know if you can braze a modern penny, the zinc might melt out of it. A nickel would probably be better but you really need to talk with someone who is more knowledgeable about metals than I am.
I just had a thought on the subject, try wrapping them with leather to increase the diameter and soften the touch.
If you want to weaken the pliers a little put the in a vise and squeeze (or as we say down here Mash) the closed in slightly and try them again. Be gentle. I have sprung my the other direction with some success.