Hi, yes, they are cut glass. It's rather hard to tell from pictures if they are American brilliant, but from what I can tell, I wouldn't doubt it. I suggest not selling them at a garage sale, but rather taking them to an antiques dealer if you want to sell (these are more valuable than garage sale finds normally are).
Nice pieces! Try to find markings if you can. When we went through my mother's estate there were many crystal pieces, some of them etched.