Hold i would EXPECT him to have them 50 / 50 , why should you have to do all the shitwork and be stuck in while he does what he wants ? Im not sure what Ow would think about having to put up with them half the time , im quite sure it would be very differant to the loveley step sisters bollocks he is describing .
I really think you need a plan , its baby steps at this stage , dont worry for now about the debts or mortgage , when i started divorce proceedings i was a sahm with no income and a mortgage that was nearly £1000 a month . Now im a student with no income with a mortage of £1000 a month ! The bank has not had a full payment from me in over 2 years . Theres ways round everything . Many banks will offer a concession for a time , theres lots of help at the moment , ill find a link.
I would really urge you to see a soliciter and take steps to get him out of your home and start divorce proceedings. You are literally living with the enemy at the moment . He is obliged to house his children , you can apply for an order where he has to contribute towards the mortgage , you will not be homeless within months or anything like that .
Think about it , he knows full well what he would be obliged to pay should he move out. He also knows he,ll be expected to have the kids a large amount of the time , where as now hes doing what he wants , going out when he wants and is quite possibly getting more credit or stashing money .Why would he want to leave ? Hes not going to unless you make him , i would make an apointment today with a family lawyer and say he is emotionally abusing you and you dont want him there .