There are plenty of lenders who will do this, sometimes it's a question of knowing how their application forms are set out that gives the clues.
Normally in this circumstance I will do a search for the best rates and then look for the lender nearest the top of the table that can cope, sometimes it takes a few calls, becuase they all have different ways of treating the 3rd and 4 person's incomes.
By all means give me a call, I'll be happy to help if I can
Adrian Garside, 01489 784022