When a union like this breaks down, factual non emotional evidence is key to progressing matters.
Here are my tips (based on dealing with a high conflict birth mother - my husband's ex wife)
Use the grey rock method - all communication needs to be about the care and welfare of your children only - nothing else needs to come into this
Set up an email account for access communication - everything to go through the email regarding the children
Always uphold the other parent infront of the children - he may be whatever, a mother may be whatever, but you smile as if they are the best thing since slice bread when you speak about them to your children or they speak to you about them.
My stepdaughter asked me one day, why I spoke so nice about her Mam when she was always horrible about me - I genuinely was stumped and just smiled and said if you have nothing nice to say then you say nothing at all. That goes for children and ADULTS.
You need to start a proper book of evidence, create a spreadsheet or a notebook to keep proper notes.
Make sure any funds paid to you are done via your bank account no cash payments
Any requests for school stuff etc to be accompanied by the evidence of why it's needed so it's clear what he is saying no too
You need to get this listed in court but you want to have your statements and evidence water tight before you go to have the best outcome
Why is there no access in his mothers home, is there room for them? I would suggest getting some form of overnight access in place to give yourself a break more than anything.
My husband does the following
€150 per week - €50 per child (now down to €100 as eldest is 20 and working he left college)
Free GP via his job
Free travel via his job
Private VHI cover for middle and youngest - the eldest was cut off at 18
Friday afternoon to Sunday afternoon every 2 week
Taxi's to and from their house to the train station (they live 4 counties away)
School fees and books all paid for by father - anything else school related split 50/50 (mother gets full BTSA)
Dental work split 50/50