As Lyonaria said, don't bother with any letters from family members regarding your relationship... UKVI aren't even ALLOWED to consider them, so they will just be ignored (and possibly handed straight back to you before they process the visa).
The photos of you are not needed either, because they are only to show you've met each other in person... and since you will be both standing there in front of them at the appointment, they will be able to see for themselves that you have met.
Just in regards to your 6 pay stubs and 6 months of bank statements:
- the pay stubs must cover a full 6 months... if you are even 1 day short of 6 months, the visa could be refused, so you just want to make sure that the dates on the payslips cover the entire 6 months (i.e. that might mean sending 7 pay stubs instead of 6, depending on the dates each one covers)
- same goes with the bank statements... they have to cover a full 6 months, and must show the deposit of every single payslip you are including