I am currently going through a divorce with ex-husband. We

Hello,I am currently going through a divorce with ex-husband.We purchased our home in 2013 for £395,000. We both currently still live in the house along with our 16 month old daughter.
We have appox £230,000 left to pay on the mortgage.My ex-husband has agreed to accept £20,000 as a full and final settlement for his share in the house and I will live there with our child.I am going to borrow the £20,000 from family members so I can buy him out.I have contacted the mortgage lender (Virgin Money) to advise them of the situation and to request that my ex-husband is taken off the mortgage. Virgin have refused this as my salary alone would not be enough for Virgin to lend me the remaining £230,000 (balance).To get around this issue my sister has agreed to come onto the mortgage with me which Virgin have accepted. We just need to fill in a “Change of party’s request form” to remove my ex and add my sister.To make this legally binding my ex and I are going to submit a “Consent Order” form to the court. We are using an online company to assist us with the application.My question is this… The divorce company have told me that we cannot mention my sister’s name on the consent order as she is a third party. So how do I get around this? This is very important as I need this to be water tight and I cannot afford my ex to challenge this at a later date because of a technicality.Is it ok to put on the consent order form that I will just be buying my ex out for £20,000 and not mention anything about my sister?Please advise.