Molly wasn’t, but her maiden name is Prewitt, and I believe there were two Prewitt brothers who were in the original. I don’t think it’s a huge leap to assume they were her brothers.
There are loads of careers in the wizarding world, it seems. Bill Weasely works as a curse breaker in Egypt for Gringotts Bank-the Egyptian tombs are full of old curses and thus, they need to be taken care of before exploring. Charley Weasely works with wild creatures-dragons in Roumania. So you’d need someone to study wild creatures like dragons and unicorns and all that. And then there are aurors-the dark wizard catchers-I guess a kind of wizarding FBI. You need people to help fight vampires and trolls.
And then there are muggle-like careers, like Madame Malkin, the seamstress of Diagon Alley. I’m sure there are wizard artists and cooks, and wizard engineers who design brooms and flying carpets, and wizard vehicles like the Knight Bus. Architechture seems different in the wizarding world too.
There are healers at Saint Mungos and I’m sure there are wizard lawyers.
I’m guessing instead of college, they do apprenticeships. Thus Percy was working for Crouch at the ministry, and learning by doing.
I think Hagrid had a good point about the Muggle world wanting magic for everything. They’d expect wizards to be their slaves-“Well, can’t you do THIS by magic?” It’s been shown that the wizarding world has problems too-dark wizards, and dangerous creatures, and politics. The muggles would probably never do anything on THEIR own, either.
I’m thinking that wizards and witches don’t get Muggle diseases like cancer or AIDS or anything, so it wouldn’t be much help to Muggles.