Hello, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question.
You would be best to raise the money by a mortgage on your buy to let properties as the interest element of the mortgage repayments would be allowable against the rental income for Income Tax purposes.
That would be my advice to you in this situation.
I do hope that you have found my reply of assistance.
Delighted to have been of assistance, Claire.
Thank you for your support.