Hi, sorry you are going through this.
Right now you need to manage your expectations about how long and complicated this process will be. Before you start making any decisions, do some background reading on different scenarios and possibilities.
I found th guide on advice now.org really useful. Legal queen on YouTube also gave me the correct current info - family law changes and will meaning people will give you the wrong info.
I am nearly 2 years on from your situation so I will outline how it happened:
Decided I wanted to separate with a view to divorcing.
Suggested to ex that we nest from our family home while we resolve living arrangements/property/custody. He initially agreed to this but backed out later.
Looked into potential shared ownership options.
Discovered I can't buy shared ownership whilst financially committed elsewhere - in a mortgage or lease. I also needed capital for a deposit.
Ex refused any financial etc discussions- this went on for a while. If I could have moved out at this point I would, but had no options.
However at this point I also was lucky to have a large one-off bonus from work. In went into my bank account, similar to your family gift.
Ex still refusing to discuss. I consulted solicitors who always pushed me to force a sale of the house and get maximum cash. This isn't what I actually wanted though.
At this point I felt stuck- I filed for divorce and also found a brilliant mediator who achieved what I couldn't do- getting my ex to discuss finances and arrangements with me.
Four mediation sessions over several months lead to this arrangement:
Ex stayed in family home and took over ownership.
I bought a shared ownership house using our 'liquid asset' savings, my bonus, and a mortgage.
I have a percentage 'charge' against our old family home. This is sometimes called a mesher order.
Kids spend 4 nights with me, 3 with him.
We used Amicable as joint solicitor to draft court paperwork.
Divorce not quite final yet, probably another 2-3 months
To answer your question about the gift from family- yes it is a joint asset as long as you are married, as was my bonus from work. It was be counted in the overall division of assets. You will need to disclose everything financially.
I got my SO house after we had to finalised our agreement with he mediator.
But finances can be reviewed until that final order is submitted to the court.
To make things easier, I had some help from family on the form of them buying furniture, white goods.
I vastly underestimated the costs (and effort) of setting up a 3 bed house from scratch, and didn't work this into the financially settlement but I wish I had. It cost roughly £8k even on a budget with second hand items.
I also underestimated the toll of living under the same roof with someone after separating..if you can organize alternative living, even temporary, do that.
What your are trying to do is possible, but you need think carefully about how you want things to play out, what's best for the kids and then be honest with your husband. Mediation was right for us, but if he is volatile you will need to spend money on solicitors so factor this in to your overall picture.
All of the above is not for the faint hearted. To say it has been a hard, gargantuan effort is an understatement. I also had a lot of luck, supportive colleagues and a decent paying job. You'll need every possible support around you that you can gather. I am not the same person I was at the beginning but I will recover on a new and better way.
Good luck op!