Some quite interesting setups, arrangements and a lot of variety - it is a complex problem.
My original partner of 35 years dealt with everything and I just paid her a fixed, agreed contribution towards our joint costs. Since she passed away, I have had two brief partners join me here, now heading towards a third. Neither of the the first two showed any real sign of integrating, both seemed to just be looking for cheaper accommodation than that which they had, or that's the way it soon appeared. Neither had any property, or much in the way of savings. All I expected from them was a contribution of £120, but both seemed to slightly resent being expected to pay. All I had asked for was a contribution towards the basic running costs of everything included, so I wouldn't be keeping them, rather than the true worth.
#3 is an entirely different fish kettle, in many ways - not least her attitude towards me is so very different. She has property, but also debts (not her fault) that she cannot meet, she is struggling just to meet just the interest charges on the various debts. Her Interest Only mortgage ends in two years, when she would need to find the several thousand to pay the mortgage off. Unable to meet that, they would repossess and the mortgage plus Charges against the property amount to around half the value of the house.
What I suggested was, if things work out between us, her best way out was to sell her property, pay off all her debts, move in with me and contribute £120. She could then live happily worry and debt free. She agreed moving in here was what she wanted, but she didn't want to give up her home - still paying the debt interest, she wouldn't be able to contribute here. I made it clear, that whilst I was more than happy to share my home with her, I wasn't willing to have her here being kept for less than it costs - no matter how well we get on (and we do get on well), it has to be viable for us both, not just her.
She has had several changes of mind about it. She is very religious and finally entered into a discussion with the her church leaders, without mentioning me or my offer, who have advised that her only sensible way out is to sell up and pay her debts off and find alternative accomodation.