Brian has made a will which leaves all five of the Home Farm offspring well provided for.
Alice should be able to support herself well with her engineering qualification, and she has made a very good choice of husband (unusual for a woman from that branch of the Archer family) who is also doing well for himself and looks likely to stay around. Over and above that, she stands to get a holiday cottage and some money that Peggy put in trust for each of her grandchildren a long time ago (when she was worried about them after Brian's affair with Siobhan).
Kate also gets a cottage and she also has a husband who can support her and her children because he works hard and is getting on well. She has her worthless certificate from the University of Felphersham and is also building some sort of career. She doesn't need much money nor does she deserve any, given that she is a nasty piece of work.
Debbie seems to be making a lot of money (remarkably, given that she has no qualifications), she is single and childless and living in tied accommodation (probably), so we have to assume she is able to save a large proportion of her salary. She will be absolutely fine financially from her own efforts, but over and above that, Brian adores her, so she will in due course inherit a large chunk of Home Farm from him.
Adam is married to a man who can also support himself and it doesn't look as if they will ever have children. They own their own home (with a mortgage) - didn't Peggy help out there? Can't remember now. He is not Brian's blue-eyed boy, but Brian has promised to leave him a big chunk of Home Farm too.
Ruairidh is a child, so who knows what his future holds as yet, but he is also promised a good inheritance from Home Farm.
James is in clover financially, as he stands to inherit most of Ralph's money (which is probably in trust for him).
However, none of them is going to be happy about this new will, except Tom. That's why this is such a clever move from the SWs. At last, something that will genuinely Shake Ambridge To The Core!