How to merge Multiple Existing Help centers into 1 Zendesk Multibrand account

We have a wonderful fantastic but old version of Zendesk here:
https://algofuturestrader.zendesk.com 

This is an awesome help desk and we use Chat and Talk  and the help desk is a life saver for all of use internal and external: https://algofuturestrader.zendesk.com/hc/en-us

We use the classic web widget  on our website and the help center  -  its simple quick and perfect for our end users to quickly get support or find an article.  We want to keep this we do not want to lose this -we do not want to have to use the new widget  and lose the classic.

We also have these:

http://microtrends.zendesk.com/

http://algotradingsystems.zendesk.com/

This is a new flavour of Zendesk  - it does have a help center but we dont care if we delete all and start again.

We also have this for the future to add:

http://alphawebtrader.zendesk.com/

Question

We think it would be better if we use multibrand Zendesk - but the questions is then how to get all these into 1 account.?

Should we cancel: http://algotradingsystems.zendesk.com/
then upgrade https://algofuturestrader.zendesk.com
then add these as new domain/brands
http://algotradingsystems.zendesk.com/
http://alphawebtrader.zendesk.com/\

or is there a magical way to make this happen?

for example specify a main ZD Account then have the other existing linked to it  - via ZD tech support etc?