Sulfur smell in one hot water heater, but not the other hot water heater
Your crawlspace Water Heater's Anode Rod is shot. This can be replaced at minimal cost compared to a new water heater by a plumber or HVAC guy or by you with some good straining on a long breaker bar...AFTER the Water Heater's been turned off, de-pressurized &amp; very slightly drained.

Solid or Segmented Anode Rods, depending on "ceiling" clearances, can be obtained at Home Improvement or Plumbing Supply places. If one Water Heater went the other could be close behind &amp; should be done as well, since checking it is the time to just replace it. There's nothing wrong or bad about replacing it too soon.