Water consumption increase as younger females age into the teen years.

I have a large house, a large family and two gas heaters (slightly smaller in total than your 105). The reality is that there isn't enough hot water for everyone to take showers one after the other or all at the same time. I'm not changing anything, it's easy enough to deal with.

First thing for you to do is to turn back up the temp (135 is safer than 140). If you can't get showers staggered a bit, you need another tank. There are few homes with enough hot water capacity to serve so many showers or baths in a short period of time. And, frankly, having that much capacity for just an occasional need seems wasteful to me.

I had a few more thoughts if this is an electric heater. If not, please ignore the remainder of this post.

I read somewhere in the recent past, maybe this forum, that the "bottom" heating coil in an electric water heater is not at the bottom but is maybe 10-15 percent of the tank's height up from the bottom. If so, you're starting out with perhaps 90 gal hot and 15 gal cold in a 105 gal tank.

Also, water heaters have a spec called "recovery rate". It's how many more gallons of hot water can be produced each hour from cold water. A gas water heater typically can recover about 1 gal per hour per thousand btus. So, a 40000 btu 50 gal tank would recover perhaps 40 gal per hour, and so could supply 50 + 40 = 90 in the first hour.

Electric water heaters have very slow recovery, what's listed for the Marathon electric is 17-20 gal per hour and total supply of 104 gallons for the first hour. Compare this 104 to 90 x 2= 180 (from two gas 50 gal tanks) and you'll see that yes, you have much less hot water now than before.

Turn the water heater to the hottest setting and that should fix it. Everyone is afraid of getting burned but if you dont have babies it should not be a problem. Your hot water will last much longer that way.

Hopefully they solved this issue 3 years ago when it occurred.