2 Turbos gone because of lack of oil supply? Head has just had to be redone because valves and pistons touched because the alternator belt went and knocked the timing belt out of sync. Could the head have something to do wth the TURBO oil supply.
I'm sure the turbo has its own feed direct from the pump so my guess would be faulty pump or blocked feed/return pipes as long as the pickup side of the pump is ok.
or the turbo oil drain line blocked also possibly, most garages or turbo repair places will fit new feed line and drain line or no guarantee for new turbo.
i think there may be micro filter in the feed pipe somewhere, drain pipe is just open pipe back to sump.
either blocked = no oil flow
was it bearing failure on both turbos?