Hot Water Pressure Issue

[Barry Kulig]

I live in a duplex and I've noticed that the hot water pressure in my unit goes down when my upstairs neighbors either use their shower or use their washing machine in the basement. There are two hot water heaters in the basement but I am confused on why this is happening. I'm a single guy and the upstairs is a family of 6 and I do not want to be paying for their hot water. Would anyone know why this is happening or possible solutions?

Thanks,

Barry