Hi Marilyn - it's forms DJP, RX3 and ST5 you appear to need here as there's no 'transfer' of the legal ownership involved
As you were joint legal owners the legal ownership passed to you following the death
The 50% share/tenants in common relate to the beneficial ownership, presumably protected by way of a form A/joint ownership restriction on the register hence the forms RX3 and ST5 you refer to
Devolution on the death of a registered proprietor (PG6) - GOV.UK