Yes, a mortgage can be held by as many people as the lender will allow. I can’t speak for the world, of course, but here in the UK there’s certainly no legal restriction limiting the number of people that are co-signatories on a mortgage.

Our mortgage broker helped us find the best deal for us: he said that having three co-owners did reduce the number of available mortgages, but not by much. One side-effect of the whole thing, though, was that we had to fill out our application form on paper because the bank’s digital application forms weren’t built to accomodate more than 2 applicants on a form. [Boo! Mono privilege! etc.]

Having three incomes significantly improved the amount of money that we were able to borrow, of course, and while we naturally needed more money (in order to buy a bigger house!) we’re still making savings by having more people making use of our shared living spaces, etc.

Speak to a mortgage broker. If you’re in the UK, I’d be delighted to recommend ours, who was incredibly understanding: just drop me a PM.