How many gallons / litres is your home water heater?
We live in a suburban 4 bedroom detached home. I find that after my wife and kid shower, I’m stuck showering in cold water.
Are they using too much water or is my water heater just not big enough?
Edit: not my photo. We currently have a 50gal tank.
Get it serviced, the most common cause of lack of water is sediment buildup around the heating elements.
If everything else is fine and the kids are older, turn the heat up. The tanks are all designed to go up to 140F. However by default the setting is lower in the US to prevent scalding 120-125F.