You can split expenses with YNAB. So you can either use one ore more categories called 'House expenses' & 'Money Owed' and split the expenses between those as you require (50/50, 70/30 or otherwise).

Personally though I've not seen it recommended by others, I categories the full expense to the category. And then when I get income from my housemate or who ever, I categories that income against the same expense category which leaves me the net and true out of pocket expense that I incurred.

Split it in half if it can be quantised. If not then read game theory on watch some lectures on it. Game theory has a topic where the splitting in such cases is discussed.