When applying for a personal loan, what do I claim my expenses are ?

If the mortgage is in your name then it a monthly expense of yours. You can tell them you only pay half of it but if you are named on the mortgage then they will count the whole thing as an expense of yours (they don't really trust you - are playing it safe). Just tell them the whole story and they'll figure it out but they may count some of the expenses as entirely yours.

Say what the expenses are and that you pay half

Just your portion is truthful and fair. And utilities don't matter, I don't think. But lenders do want to know about other debt like auto loan payments, student loan payments, and credit cards. Fixed monthly payments for debt.