Have Tax Questions? Ask a Tax Expert for Answers ASAP
Thanks for your question - I am Sam and I am one of the UK tax experts here on Just Answer.
No there is no way to avoid stamp duty, on either proposal and I should also advsie your mother in law will be liable to capital gains tax on this transfer - whether she transfers all or half to you as she is disposing of all or part of a property that has never been her main residence.
Capital gains would apply even if there was no mortgage on the property and she gifted it to you - I am afraid there is no avoiding thee charges unless she continues to pay off the mortgage and transfers it through her will ( but then if her estate of more than £325,000 then there is Inheritance tax to consider)
Let me know if I can assist further