Since you didn't have the smell before you went away you may have sulfur reducing bacteria in the electric WH. Check the toilet tanks to see if there's any slimy stuff in there.

Note what the temp setting is on both WHers. Turn the temp on both water heaters up to 140 for 2 hours.

Be VERY careful if using hot water during this time cause it will be REALLY hot but best not to use any hot water during this 2 hours..

After 2 hours set the temp on both WHers back to where it was. Open all the faucets everywhere till the smell is gone.

If that doesn't solve the problem then your entire plumbing system will need to be sanitized. If you have water treatment equipment that will need to be sanitized also.

Lurker nailed the problem. If the tank has a cutoff valve on inlet,I might close the valve and drain the tank through a garden hose connected to drain on lower tank. To break vacum while draining,open the nearest hot facuet or open t&p valve. Refill and drain once more then do exactly as lurker said. The logic is to flush out much of the alge ,leaving less alge to kill off and doing a routine sediment flush in the process.