In the startling position of feeling a bit sorry for my MIL today!
MIL has a younger brother, Steven. She always got on best with their father (now deceased), he with GMIL. Steven fell out with GFIL over not wanting to go to Sandhurst. At around the same time, MIL got pregnant with DH - very young and out of wedlock - and GMIL didn't really speak to her for 25 years!
Just after he left uni he had a bad drugs experience (LSD I think), and was unable to work for almost a decade due to flashbacks and general trauma. GMIL doesn't know it was LSD and thinks he was in a car accident MIL and GFIL kept it from her. Steven lived with the GPILs during this period. Eventually trained as a horticulturalist and is doing fine now though still a bit odd.
The GPILs family has a very old and venerable history - not talking landed gentry (not for the last few generations anyway), but an unbroken line of distinguished army officers going way way back. Following GFIL's death, GMIL (she married-in to the family), is now the custodian of all this military history and other assorted antiques, silver, fur coats etc etc. She has loads of fascinating stories.
Steven has been with his longterm partner for 20+ years, they have not had children (and won't, both nearing their 60s now). GMIL is fond of DH though didn't have much to do with him until he was a teenager. GFIL used to take DH on long country walks and orienteering and so on, probably hoping the army gene had just skipped a generation. So he and DH were much closer than GMIL and DH.
DH and I have two sons. They have the family name (as DH has his mother's maiden surname), and are the only descendants of that particular branch of the family. At a family event over the weekend, MIL said she'd caught MIL throwing away GFIL's army uniforms and some clothes from the 1900s. I work in a museum and said oh my goodness, what a tragedy, would GMIL like me to come and help her go through what's left?
GMIL said she'd already given 'boxes' of stuff - medals, paintings, uniforms, nothing that would be valuable to anyone - to charity shops in her local area "because there's nobody to leave it to now Steven won't be having children". All objections met with "well it should be up to Steven".
At the DCs christenings she gave them family silver (child-sized cutlery, beautiful, one inscribed with GFIL's name), saying "of course these should really go to Steven".
And she's told Steven that she's leaving everything (house, money, anything that's left after these charity shop trips), to him as he's the 'heir' - he thinks this is completely fine and has told MIL (and GMIL), that he doesn't intend to rewrite his current will which leaves all of HIS stuff to his partner.
GMIL says this is because of male primogeniture and completely the right thing to do as DH doesn't really 'count' as a male descendant of GFIL as he was born out of wedlock - now, I've watched Downton Abbey as much as the next person but really?!
And okay fine, if there was huge estate then presumably it would be handed on to DH after Steven passes away. But there isn't and nobody has any intention of doing male primogeniture anyway!
It all sounds to me like GMIL is letting MIL know that she's still in the doghouse. MIL is distraught as lots of the precious memories of her DF are tied up in objects/photos/etc. Feel sorry for my poor DCs who are reminded at every turn that any family stuff passed on during GMIL's lifetime should really be going to great-uncle Steven, too.
I don't know any other 'old' people (my own GPs all died before I was born sadly), but surely this is totally bonkers?