It is often forgotten (including dare I say by lawyers who are not specialist divorce solicitors) that whether people have been married or not and whether there is yet a divorce or not does not stop the Court dealing with the housing for and sometimes the child maintenance involved in the case. The Children Act provides for, effectively, a financial settlement for children and often child maintenance too.
Judges will often make Orders allowing the children and therefore the parent with day to day care, to stay in a house--or have a house provided--until they are 18. This can even happen when the person providing the house is not the natural parent of the children.
Sometimes people deliberately refuse to marry and "just keep living together" as they think that will avoid a financial settlement.
So where there is someone owning a house in their own name, not married, living with someone who has children from a previous relationship they may feel "safe" from claims if the relationship breaks down. But they may well not be.
Andrew Woolley, Family lawyer