Fiancee has died his family are after his estate - what can i do?

[confused.co]

My fiancee has recently passed away and less than 4 hours after his death, his family raised the question of who is his next of kin and who will have the estate?

I was engaged to my fiancee for 4 out of the 8 years that we were living together unfortunately we both had our own homes and had did not have either names on mortgage, bills and life insurance documentation.

I know and mutual friends have said that he did not want his family benefitting from his death - he hadn't seen his next of kin (biological mother) for 30 years and had no relationship at all with his family

Where do i stand on this? We had no children together and all of his belongings are in my property for example car keys, savings books etc, does this mean that whatever he had which is in my property belongs to me??