I have a similar case with a Dyn11 33/0.415 KV transformer connected reverse fed to a LV Switchboard which totalizes 4 LV Gens onto the same bus.
What is the best and safest earthing scheme that has to be adopted?
This is not something that you're going to resolve with free Internet advice from total strangers. It's a complex issue with a lot of unknowns. Without more information, we'd just be guessing. There's no shortcut here. You may have to engage someone with more experience.