Separation and settlement regarding family home.

My sister is currently going through a nasty separation, her ex is now living abroad, her youngest is 13 and is living with her in the family home. The family home is in both names, she is trying to get her ex to relinquish his claim on the family home, besides getting his consent what does she have to do ? i.e. what papers does she have to get signed, does she have to register this with the mortgage holders or the land registry ?

Will have to get the banks permission to remove him from the account, this is proving a huge stumbling block for many people as the bank will underwrite the loan again based on their present criteria which for many people means they will not qualify to have the mortgage in their sole name. So maybe before you go to the bother of other stuff check with the bank first if they will allow it.

This may be naive, but would it suffice to get a letter signed and witnessed detailing her ex's willingness to relinquish any claim on the family home now or in the future and once having this, then deal with the bank and other institutions.

I don't think this document would be any good. For a transfer of a house you have to have a 'family' home protection act document signed as well. The advice of a solicitor should be sought. But at the end of the day if the bank won't agree it there is no point.

Is it possible for a person to bring a case for legal separation with out engaging a solicitor. I.e is it acceptable for them to represent themselves. If so how does one go about it?

Yes of course you can represent yourself in any court action. As to how one goes about it, you will have to do some research and work out how to do it.