3 Residential Mortgages

If the families in those properties are paying rent/the Mortgage to your friend. There are lenders who may disregard the Mortgage repayments providing the rent is 100% (or more) of the mortgage repayments.

Your friend is in a very difficult position, if her friends stop paying rent, there is an argument that they can not be evicted - especially if they paid the deposit.

Your friend will need to be declaring this as an Income I suspect which now means she will be taxed on it and rent from 3 properties plus a job probably means 40% tax.

This is a massive mess and I would debate speaking to an accountant/tax advisor before buying a home of my own.