It’s always hard to give suggestions about a case as we do not know the full details and there are no formula answers. In the hope it might be helpful here are some ideas.
Assuming you are dealing with the excluded person, I have found that in difficult relationship issues one choice a person can make is not to say or do anything that makes the situation worse. This may seem at first like a negative plan but it has a very positive motivation.
My guess would be that the exclusion is not simply due to tidiness and such like. Your client may be holding back some information or might not even be aware of the implications of his/her behaviour. Inviting more detail about the client’s interactions with the family (and family values) might unearth more. Has this person betrayed some deep seated family value (and maybe not even realised it)? Are the family values somewhat fundamental? Hoping this is helpful!