The mortgage balance is around €30,000.
The equity in the house is around €220k (250 - 30)
So you would need to pay him €110k and take over the €30k mortgage.
So you would need to borrow €140k
It's unlikely that a lender would give you this as it's almost 4 times your salary and you have three children.
You are presumably talking to a solicitor and all the following are in the context of an overall agreement on maintenance and any other assets, including pension schemes.
Option 1 Buy his half now and pay out of the maintenance.
You do all the legal work and end up owning the house.
You will have a mortgage of €30k in your own name.
You will owe him €110k .
Let's say he has to pay you maintenance of €1,000 a month, you pay this over the next 110 months.
You would have to pay the mortgage for the next four years and you would have no maintenance for the children, so this is not a good idea.
Option 2 You take ownership of the house in exchange for your share of his pension fund.
If he has a pension fund, you could take your half of the house in exchange for reducing your share of his pension fund by €110k.
You own the house outright, but you have no income in retirement.
This does allow a clean break and no dispute over pensions, early retirement, lump sums, etc.
Option 3 Your dad buys his half now
There is absolutely nothing illegal about this. It's a bit inefficient for tax purposes as your father would be paying 50% tax on payments from his daughter and you would be getting no tax relief. Your father would end up paying CGT on any gain in the value of the property if it's sold.
Option 4 Your dad lends you the money now to buy his half
This is much cleaner. You own the house and you owe your father the money rather than owe it to the bank.
The downside of this is that it takes the pressure off your husband to pay maintenance. He could argue that you are living rent free.
Option 5 Remain as joint owners of the house and agree to sell it when the youngest is 22
This seems the most likely outcome as your husband is obliged to provide for his kids.
You continue to pay the mortgage jointly.
Your ex pays you €1,000 a month which you spend on your children which is what it's supposed to be spent on
After 10 years, you put the house on the market and split the sales proceeds.
You could agree a clause saying that you had an option to buy the house after 10 years at its then market value.
Let's say that the house is then valued at €300k, you would then pay your ex €150k.
At that stage, your dad could get involved if you have not saved up the purchase price by then or if you can't get a mortgage.
Check with your solicitor, but I believe that as you own the house jointly, if either of you dies,the other would get the house, which is presumably what both of you would want.