Buying out my mother in law

I live with my partner of 5 years in a house which he bought shortly before we met. He took out a mortgage for half the value of the house, and got a loan from his mother for the other half. I would like to buy her half. I have half the value of the balance of the loan in savings, but I'm wondering how I should handle the other half. Should I take out a loan from the bank, or a loan from my own mother? I planned on going to a financial advisor, but I figured I may as well ask here to come up with a skeleton of a plan first.

Does your MiL legally own 50% of the house?
Or does your partner own 100% and separately has a personal loan with his mother?

Depending on the answer, you would have to buy out either the mother or your partner (and then he can use that money to pay his personal loan).
If you have been cohabiting for long enough you may already have some claim on the property... maybe something to check with a solicitor

Maybe give all the information as follows

From your description, it seems

1) Your partner owns 100% of the house which is worth : ?
2) He has a mortgage of ?
3) He owes his mother ?

His mother is not on the deeds of the house.
His mother is not on his mortgage.

How much savings do you have?

Have you any plan to get married in the short or medium term?

Is your partner solvent financially?

Brendan