I am installing 400 amp service with two 200 amp disconnects and then running direct burial alum wire to another 200 amp disconnect 100 feet away due I need to run a ground wire in that underground wire bundle to connect to the two disconnects as long as I separate 200 amp disconnect ground and the nuetral at the last diconnect

You DO need an equipment grounding conductor between the service equipment (main disconnect) and any/all panels.

There used to be certain conditions which allowed a 3-wire feeder omitting the equipment ground, but this has been removed from the code.

Thanks for your help

Isn't that what I stated here:

https://www.askmehelpdesk.com/electr...ct-466657.html