I got it to work!
This is how I did it :
The database settings are set to the remote db [As per advice by dismounted].
Using the advice at :
https://vborg.vbsupport.ru/showthrea...ht=datamanager
I was able to write a user directly into the database across sites. I expect login etc could work the same way, but I just wanted the users to have the same login on site and forum.
Thanks for all the help/adivce.