OCI Renewal for 2 kids

Hi, I am planning to submit an OCI renewal for both my kids who have new British passports. The guideline pertaining to this is very unclear on what documents are needed and hence, some advice is appreciated. I am planning to carry the following for each application:

- Child's old+new British passport + OCI card
- 1 Photocopy of the above
- Parents' British passports + OCI card
- 1 Photocopy of the above
- 2 copies of Application form (Online Misc form) for each kid
- 1 Declaration form for each child
- 2 photos
- Authorization letter from my partner as he will not come for the submission
- Marriage certificate copy + Birth Certificate copy
- 2 self-addressed special delivery envelope per application

I have been told that all photocopies should be attested by both parents.

Is this all that's required or is there anything else that I'm missing?

Thanks so much for your help!

EDITED to include more detail:

- Child's old+new British passport + OCI booklet
- 1 Photocopy of the above including the Visa copy in the old passport
- Parents' British passports + OCI card
- 1 Photocopy of the above
- 2 copies of Application form (Online Misc form) for each kid
- 1 Declaration form for each child
- 2 photos
- Authorization letter from my partner as he will not come for the submission
- Marriage certificate copy + Birth Certificate copy
- 2 self-addressed special delivery envelope per application

1) I will advise to carry Original Marriage Certificate and Original Birth Certificate also just in case along with copies.
2) Number of envelopes need to be made sure. One application requires two Special Delivery envelopes. If these are two separate applications, then 4 Special Delivery Royal Mail.