help me make sense of this

In 2016 Jason and Kylie purchased Ramsey View together as their home with the help of a 200,000 mortgage from BetterBank Plc. The property was registered in the joint names of Jason and Kylie. Soon after moving in Jason injured his back and was forced to retire from a promising music career causing Jason and Kylie to struggle financially. In 2017 Jason's Dad, Alan decided to sell his house and moved into Ramsey View to act as Jason's carer. He agreed to use 100,000 from the sale of his house to pay off half of the mortgage. Jason and Kylie continued to pay the remaining mortgage from Kylie's wage. In 2019 Jason and Kylie were asked about investing in a recording studio business with Jason's old manager. They approached BetterBank Plc seeking to remortgage the property and were told they could borrow an additional 100,000 on top of their existing mortgage. They did not tell Alan about the mortgage and at the time the new mortgage was taken he was on holiday in Australia. The surveyor employed by the BetterBank Plc had recently viewed a similar property and so decided to only look at the outside of the property for any structural issues. By June 2022 lockdowns had caused the recording business to go bankrupt and Jason and Kylie had not paid the mortgage for three months. BetterBank Plc have sent a letter informing Jason and Kylie that they are seeking possession of the property in order to sell it. Alan has just found out about the mortgage and is worried as he cannot afford to buy anywhere else.

a. Advise Alan as to whether he has a successful claim to any interest in the property and whether he can prevent BetterBank taking possession. Include in your answer a discussion concerning the consequences of the mortgage being in arrears.

b. How would your answer differ if the property was in the sole name of Jason? Include in your answer a discussion on the Trustees of Land and Appointment of Trustees Act 1996.