and thanks Just Answer.
My name is ***** ***** am happy to assist you with your enquiry.
1. If you ar ehaving a Mortgage, then your Mother will also need to go on the Mortgage aswell as on the Deeds. This is because a Mortgage Lender insists that all parties to a Mortgage go on the Deeds and vice versa.
2. If your Mother's Life policy is written in trust grandchildren, which is perfectly normal and easy to do, then these monies from the Policy will pass to them automatically. Therefore, your Mother would need to do make a Codicil (an amendment to her Will), if she does not then want them to inherit 50% of whatever else she leaves in her Estate. A local Wills Solicitor can deal with this and will cost approx £100 plus VAT.
3. Provided your sister is not financially dependent on your Mother, and your Mother has in no way promised anything to your sister/your sister has not done anything to her disadvantage on the understanding from your Mother that she would receive a cash sum/part of the Estate from your Mother, then she has zero chance of contesting her Will. It is always best Mother to put in her Will (or Codicil) the reason why she is leaving your sister out of her Will.
I hope this helps and answers your questions.