Renewing South African passport at embassy in London

My husband is South African and waiting to receive renewal application forms for his passport.
( DHA73, DHA 9 and DHA 529)
not sure if all 3 forms will be posted or we will have to print some of them

So far we gathered these documents to renew via post:
certified copiesx2:
current passport
ID book
our marriage certificate (original in Polish)
marriage certificate translated into English by sworn translator
registration of marriage form

I learned it is compulsory to register our marriage

4xpassport size photographs

Is there anything that we are missing?

We are waiting for letter of retention of South African citizenship which was applied for because we also in a process of starting to apply for British Citizenship. I don't understand why this letter must be part of the passport application since we get it from South African embassy anyway. I guess I should add the copies of it too?

Has anyone applied lately and what was your timeline? I heard that they are long delays.

Many thanks