Any bank that is making a loan is going to require an appraisal. Aside from that, a home inspection, done by a good reputable inspector, can tell you a lot about the condition of the house. Typically I think of two broad categories of house repairs/improvements. The first is aesthetic things like painting, changing out light fixtures, taking down dated paneling, etc. These sorts of things are relatively inexpensive, can do a lot to improve the way the house appears , and are generally easy DIY. The other category is big expensive stuff: structural problems, roof, furnace, new Windows, major electrical or plumbing work, etc. these tends to be expensive to very expensive and are often outside the ability of DIY.
A realtor can also answer questions about a fair sales price for the home. Your boyfriends parents benefit in selling directly to their son because they save ~7% from the realtors fee. However, if your boyfriend overpays for the house, he is saving nothing. I think there is more research to be done to determine a fair value on the house, what needed repairs would cost, and if your boyfriend wants to take on the financial obligation of owning a home.