Your joint assets are
house £700k
pensions £520k
Does she work? Her mortgage raising capacity is relevant, unless she is moving in with her new partner.
Expected split assuming both work and earns enough to support herself and get a mortgage is 50:50. The court would be unlikely to take the children into account, by the time you get round to the hearing your youngest may be 18 anyway.
So reasonable split:
You take out an additional mortgage of £350k and buy ex out, and:
You transfer £140k of your pension to her pension pot, so each of you end up with £260k each.
You could choose to give her more pension in exchange for more of the current assets, ie the house.
The car should also be taken into account if it’s an expensive one. Say the car is worth £50k, then it would be reasonable for you to offset the value of that against more equity in the house for you.
Nb if either of you are on something like a final salary pension you will definitely need to have it valued, since the real value can be many times the CETV.
Why do your adult children not pay rent, cook and clean?
And why do you pay her maintenance?