Wow that’s your problem. 80 gallons is enough for 15 people. Forty gallons is for a small family and 50 for a big family. And why would they use electric over gas? Whoever they were, they are weird. Gas is usually a lot cheaper around here but you should investigate if you have gas lines and the venting needed. I guess it depends on how they are fed to the sinks and showers - do they feed into separate hot water pipe networks or do they combine into one system? You can get tax credits to swap in a high efficiency electric water heater but the purpose of those is usually when you have no gas line or want to reduce your carbon footprint.