South African passport renewal process questions

My wife and I are South African citizens.

My wife’s passport is due to expire on the 23 November 2020.

I have the following questions relating to the renewal process:
1. Can my wife apply for a new passport now or does she have to wait until 3 or 6 months before the expiry date?
2. Are you allowed to keep your “old” passport and travel with it during the renewal process?
3. In connection with the above, we have a holiday booked in April 2020. Should she only apply for a new/renew her passport on return from the holiday?
4. What happens to the tourist visa’s in the “old” passport? Do they become null and void once the new passport is issued?
5. There are 2 documents required for the renewal application that can only be collected or requested via post from the High Commission office in London. Does anyone have experience as to whether these can be collected and completed on the day of the visit to renew the passport? Or should these be requested in advance via post? We currently reside outside of London and therefore are not able to easily travel to the High Commission office.

Any assistance with the above would be greatly appreciated. I have searched various UK and RSA sites for answers to the above without any luck.

Many thanks

1. She can apply at any time, but I would be cautious of applying too late.

2. Not sure, I believe they are sent in with the new application and will be cancelled and clipped once a new passport is issued. I remember having to send my daughters valid (soon to expire) passport when i applied to renew hers.

3. Suggest apply after your holiday as passports can take up to 6 months.

4. Yes, likely. It does probably depend on what countries they are for.

5. Yes you can pick up and complete on the day at SA Consular Service, Whitehall.

Thank you for the very helpful responses. Much appreciated!