Custody vs 50/50

Custody is an outdated term that isn't used any more. We now use child arrangements, which encompasses all the parts of a child's life and upbringing by both parents post-separation. You're right that if parents agree on the arrangements for thier children then contested court hearings aren't required.

I don't think it's helpful to look a division of a child's time between thier parents in terms of percentages. It muddies the waters and detracts from sorting out workable, child-focused arrangements. Those arrangements aren't about what you want, but about what is best for the children to enable them to spend good amounts of time with both parents.

As you are not married and own the property jointly, you will need to buy your partner's 50% share of the property if you wish to remain living there. However the housing needs of the children are paramount, and if she is not in a position to rehouse herself and the children then you need to be realistic about her housing situation. It's not enough to put her into a rented flat and agree to pay for it for a period of time, while you enjoy sole occupancy of the jointly owned property. As Wyspecial points out, this is not something your partner is likley to agree to.

I totally agree with everything you've put there Ruby. But the flip side of that coin would be me in the rented accommodation and footing the mortgage. A solution that wouldn't be feasible. Her step dad owns a very affordable (to family) 3 bed flat nearby. That option probably isn't open to me.

Don't get me wrong the ideal solution would be to sell the house and then the kids would be getting two homes. With no job and no income her ability to obtain and maintain a mortgage is next to nothing. So she would need to be in rented accommodation anyway. I want to find a way to make both parties (not happy but able to live) and move on in the interests of the kids. Inventing stories of horror and getting lawyers involved really doesn't fit that bill.