Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
How much is the house worth and how much is outstanding on the mortgage?
How old are the children
Are you married to your partner?
How much does a cheaper three bedroom property in the same school area cost to buy?
Are you aware that a phone call cost more?
In fact you are in no way financially liable for her children.
If you separate you certainly will not have to pay for her to remain in the property.
Your worst case scenario is that the sale will be delayed and you may have to wait for your share of the equity.
However given the figures and the fact that the children are not yours there is an excellent chance that a Court would still order an immediate sale if an applictaion is made.
I hope that this is of assistance - please ask if you need further details
You are most welcome