Attorney under LPA

Hi
I wish to know what signatures the Land Registry will accept on a TR1.
House owned as tenants in common.
1 owner (Mrs A) now lacks capacity but a valid LPA is in place - appointing Mr A (other owner of house) along with sons B & C as attorneys.
Mr A is to transfer his half house into a Family Trust - therefore title to be transferred via TR1 into the names of the trustees - sons B & C along with Mrs A remaining as owner of her half share.
Section 8 - The transfer is not for money or anything that has a monetary value.
Section 10 - holding the property on trust 50% for Mrs A and 50% for the beneficiaries of Mr A's family trust.
Question is what signatures will the Land Registry accept on the TR1?
Mr and Mrs A as the transferors (but Mrs A lacks capcity to sign) - transferees to be Mrs A and sons B & C.
Who is able to sign for Mrs A?  Will you accept any of the attorneys to sign for Mrs A bearing in mind that they will also need to sign in their own right?
Or will a trustee (not connected to the trust) need to be appointed to sign for Mrs A or alternatively Mr A leaving Mr A to then sign in his role as attorney for Mrs A?
I hope this all makes sense!
Kind regards
Ed

Hi Ed - please see section 10 of our PG 8 on execution under a power of attorney.
Execution of deeds (PG8) - GOV.UK (www.gov.uk)

Hi Adam

Thank you for your extremely prompt response.

So my understanding is that Mr A can sign for both him and Mrs A but it will be returned for execution by the donor (which is not possible).  The guidance then states that a restriction to protect any benefical interests that may subsist will be entered BUT does this also mean that the title will be amended into the names of Mrs A and the 2 trustees - sons B & C?

Many thanks

Ed

Ed - not quite.
The guidance you are really after relates to the LPA and what it allows to happen on behalf of Mrs A and whether the attorneys she has appointed, which you state are Mr A plus sons B & C, can act jointly, severally or a mix of both. 
That will help you with regards whether Mr A executes as himself and children B & C execute as Mrs A's attorneys for example
The relevance of the restriction is that I assume one exists, namely a form A restriction otherwise known as a joint ownership restriction. And if so and the Transfer is not on sale then the existing form A restriction will remain on the register 
The register will only be capable of being updated if a transfer of the legal ownership is successful. The existing restriction is very unlikely to have any say on that if you have Mr A plus 2 children B & C involved