I would pull them all up and have a look see at the roots. It may give you the answer as to why they aren't thriving. Look even inside the lower stem and see if it's hollow or red. Beans when sprouting (as well as growing though not so strongly) release very specific chemicals into the surrounding air, which are very attractive to some pests. The chemicals form long, hyphenated names so i'd have to look them up to list it here. However, different varieties release these chemicals in varying proportions so some are more vulnerable, some much less so.