Hello and welcome to the site. Thank you for your question.
As it is your parents' intention not to have shared ownership the options available are
- their contribution towards the purchase price is treated as a loan to you with a loan agreement in place (with or without a charge on the property). It can be interest free loan.
- their contribution is regarded as a gift to you and it is a potentially exempt transfer for inheritance tax purposes and the seven years rule applies i.e.if they survive for 7 years after making a gift to you, the gift is generally exempt from inheritance tax no matter what the value is.
Provided their joint wealth does not exceed (325,000 x 2) £650,000 on the death of second partner, including gifts made within 7 years of death, there will be no IHT payable.
More information on transferring of unused Inheritance Tax threshold can be found here
As both of you would be disposing your respective properties that are your main residence, there is no CGT payable on any gain made.
I hope this is helpful and answers your question.
If you have any other questions, please ask me before you rate my service – I’ll be happy to respond.