advice - inherited a house but mum partner lives in house

Talk to him. He's grieving too, but you've got a job to do & she didn't rewrite her will to include partner. It may be the poor soul knows darn fine every night under the beloved's roof is a treat & will agree & cooperate. Treat them with the courtesy your mum would wish, include them in funeral decisions etc if possible (even if only at associate member level) and work at staying polite as a minimum.

You may be very pleasantly surprised. You will be in a much stronger position to look for cooperation from partner &, if necessary, courts if your conduct has been courteous, considerate & tactful throughout.

Condolences on your loss and all the best with the complexities of admin amidst grief.