Four kittens were abandoned in my yard (I've only seen the mother once, when I discovered the kittens). When I discovered them, they were already very coordinated, able to walk very well, and social. I estimate they are about 5 weeks old now. They all weigh about 10 oz. One of them can eat wet food, and a very short fur one (looks premature, although it is average weight compared to its siblings) only takes a bottle, but not very well. How soon can they all be weaned to solid (wet) cat food?
I think you should start slowing weaning them now, if they really are five weeks. (Check to make sure, you don't want to wean them too early) Feed them wet food, then slowly add kitten dried chow in to mix, more, and more until it is 100% dried kitten chow this process takes about a week or two.
Notice any diarrhea or vomiting. Make sure they have lots of water. Keep to the same food/brand/flavour, they will vomit if you change. After a few more weeks, and there doing fine, I say get a checkup.