Replacing a Tenant in Common

My mother owns her house as tenants in common with my sister and would now like to give her half to me. It seems straight forward and I like to save money by doing the paperwork myself if possible. The property is in England with a valuation of £250k, no money will be changing hands. From discussions with conveyors the forms needed are AP1, TR1, ID1. However some have said RX1 also needed, is that correct?

Timothy - form RX1 is a specific form use to apply for a restriction - Notices, restrictions and protection of third-party interests (PG19) - GOV.UK (www.gov.uk)
I suspect, but only you/the conveyancers you have spoken to will know, that reference to a 'restriction' is linked to the term tenants in common and/or a restriction already on the actual register - Joint property ownership: Overview - GOV.UK (www.gov.uk)
If that is the case, and the register already refers to a form A restriction and you and your sister will want the same, then there's no new restriction to apply for. If the transfer is by way of a gift and you complete TR1 as appropriate, then the existing restriction will remain on the register after it has bene updated to show the new legal joint ownership.

Thanks Adam for your swift response. So it's just the forms AP1, TR1, ID1 and having mine and my mother ID certified? and I can submit those myself?

Timothy - any transfer is of the whole legal ownership so would be by your Mother and sister to you and your sister. So you need ID verification for all three of you
The tenancy in common/shares relate to the beneficial ownership. We register the legal ownership and that can only be transferred as a whole. Hence you have a Transfer from Mother and Sister to Sister and Brother to complete

I was of the understanding that a tenant in common could dispose of their share without recourse to the other tenant in common?

Timothy - they can but that share is only of the beneficial ownership. However we register the legal ownership and that can only be dealt with as a whole. It can't be split/divided into shares.
So if your Mother wishes to transfer her beneficial share to you and you then become a joint legal owner with your Sister, then the two of them need to transfer it to the two of you using the forms you referred to.