Who's name should go on the land register

Mum passed leaving her share of 50% of the property to her children (4) (currently with trustees) and the other 50% is my step brothers (also part of the 4) who bought my father's share when mum and dad spilt up,  He currently resides in the property which was mums wish until he should die or sell up. Thereafter the remaining siblings would benefit from the inheritance. Question is, should it just be his name on the deeds or all 4 of us?  (currently it's just his which he took upon himself to do) .
He's already stating it's his property (because his name is on the deeds) and will do what he wants with it when he dies and states he's made a Will to that effect totally ignoring mum's last wishes in her Will.
Was he wrong not to include all 4 of us on the deeds?
I have a copy of mum's Will if it helps?
Grateful for any advice please?.

Allan - it's really legal advice you need here as to how the trust was created and how the beneficial ownerships/interests work in the complex scenario you have
We register the legal ownership so for example if a joint legal owner dies the legal ownership passes to the surviving owner. The beneficial shares can still be left to others, as in your case, so it's really the will/trust that you need to be checking to confirm what's happened to your late Mum's beneficial share and how it might be handled when he passes and has his own will re his own beneficial share.
Understanding who has what beneficial share now will impact on what can also be left to others so it's important to seek legal and not registration advice

Thank you Adam