Advice please

So me (m36) & friend (f28) are expecting a baby we aren’t a couple we don’t live together but are considering moving in together just because of the baby

i get UC limit work capability and pip of both low elements and my friend receives the same and we both receive rent payments of £440 for our 1 bedroom flats atm

just wondering what would happen if we was to move in together a 2/3 bedroom house? In terms of rent rate we would receive and what effects this would have on UC?

many thanks in advance