Hi, thanks for your question. Are there any formal agreements with the joint mortgage holder regarding payment of the mortgage and process to sell - for example a deed of trust?
Thank you for confirming. In relation to the tenants, you are allowed entry upon at least 24 hours written notice. You should also be pursuing eviction so that this does not impact any future sale - eviction of tenants can take between 2-9 months and should be pursued immediately if the process has not started. If you are not pursuing rent arrears, you need to first give them at least 2 months' notice to leave and once this expires, if they have not left you will be able to apply for a possession order, more information here: https://www.gov.uk/accelerated-possession-eviction
In relation to selling the property, if your mother in law is also on the title of the property, and she does not agree to sell the property, you will need to pursue a court application using form N1 and a £355 court fee to your local county court.
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