My parents registration

My father brought their property in 1985 in his name only, there is no mortgage left, he has the schedule of deeds dating back to 1965 and previous owners, he also has the conveyance date year of purchase 1985 
he now wants to add my mother, his wife since 1973, 50/50
i have the forms AP1 -
Q5 - what’s documents do they need to send ? 
Q7 - can my sister apply for them?
Q14 would her name need to be added here?

FR1 form
Q7- can my sister apply or better with my father?
Q14-16 - do I have to fill in these if its voluntary registration ?

TR1 - do they need this form?

DL
- is my fathers nearly 40 year old schedule of deeds original enough?
- his 1985 conyevance ?
- register of local land charges 1985?
- original land charges search results 1985
- Britannia agreement & undertaking with my mother added as occupier including my father of their home.
- he has the original legal charge of mortgage (Britannia) 1985
- also 1998 statement of account when mortgage paid up x 3 

any other information would be gratefully received 

Daniel - I assume the property is unregistered hence your Qs. If so then form AP1 is incorrect. You need forms FR1 and DL and the transfer will trigger the need for compulsory first registration - First registrations (PG1) - GOV.UK
I have ignored the Qs re form AP1 as a result
Form FR1 - anyone can apply and see PG 1 re what deeds/documents are required. It's a compulsory first registration so both your Father and Mother will need to have their identities verified. If your sister completes the application then she too will have to have her identity verified.

Yes this property is unregistered.. 

That’s the only forms FR1 and DL and ID x 2 (if sister doesn’t apply) I need to submit 

Daniel - correct. Do read through PG1 and then decide if this is something you/your sister want to do without legal assistance/advice
For guidance on transferring the ownership then see Registering land or property with HM Land Registry: Change the registered owner name - GOV.UK
Note that form AP1 should be replaced with forms FR1 and DL

FR1 

Q3 - 

I have 3 older scale drawings outlining property from district council pre 1985 

would any of these be sufficient or could I just use address of property and ordnance survey map?  

This would only be to register both parents as owners 

Daniel - entirely up to you as it's all about which extent are you trying to register. You can just use the address and then rely on what OS currently shows as it's physical extent. See PG 40 sup 2 for guidance - Preparing plans for HM Land Registry applications (PG40s2) - GOV.UK 
Correct - Father is transferring the whole legal ownership from himself to the two of them  - that's what you posted previously

Question 

if I apply for the registration for the first time and in joint names for parents as owners, is this then legally binding, so that I don’t have to transfer it onto the title deeds also? 

Daniel - I don't quite follow your thinking/Q. Sorry
Your Father transfers the legal ownership to himself and his wife
The transfer triggers the need to compulsorily register the property in their joint names
Registration then creates a registered title that is then the proof of ownership.
The old deeds/documents are no longer that proof and the registered information is the 'title deeds'
If you are unsure of what's required, why and what impact it has then please do seek legal assistance/advice. The property will perhaps be their biggest asset so getting it right matters