Advise needed to change shared ownership without fall into Tax difficulties.

[Mr.R]

Hello,
I own a house equally share (50-50) with my old mother, says it worth 1 M. I married a Thai lady for 8 years, she is now holding British passport and earning the same with me as we run our small business. I lived in this house for over 30 years and pay most bills for my elderly mom. Now we are moving in with the children, I and my mom want to put her name on the deed. Another reason is the house is in very bad state as my mom never wanted anyonthing done in her house, neither cleaners nor builders. But now decided to re-do the whole house and we need to borrow money from the bank by putting the house as guarantee. I think it would be good idea to get the mortgage in both names so we get a bit more money.
The big problem is we wanted to be sure not fall in any Tax difficulties (as now we paid tax even more than we have to spent for ourselves), like having to pay more income tax, more Inheritance Tax, Capital Gained Tax or other kinds of Tax. So please advise what is best solution in my circumstances.
Any advice will be more than appreciated and thank you.