Good afternoon, I bought a house about 6 years ago, this house has a granny flat that I am renting at moment, the granny flat is completed separated from the house, the only thing we shear is the main cold water and 2 radiators that works when I turn on my heating in my own house.
I was thinking in add a timer control in the granny flat so they could turn on the heating at their own desire time, I was wondering if I could add a second water cylinder in the granny flat so we could shear the hot water as well.
Thank you very much I will really appreciate any advice, sorry about my English, hope you got the idea.

I was thinking in add a timer control in the granny flat so they could turn on the heating at their own desire time, I was wondering if I could add a second water cylinder in the granny flat You have combined two questions in one sentence. First you talk about heating. You want to install two thermostats on the same heating system? How's that going to work?
Next you want to install a water heater so the Granny unit would share hot water with you. Isn't that what you're doing now? I don't like either idea and here's why.
Two thermostats and one boiler. Your house is warm and the flat's cold. They crank the heat up. What happens now? You burn up while they're cozy?
Adding a second water heater and combining the two so that you share. Who pays what? You have a family using hot water while just one person in the Granny Flat. How fair is that?>
NO! Them only sensible 6thing to do is isolate the two systems. Two water services and separate water, electrical and heating systems. That way if you ever wanted to rent it out you'd be covered. Good luck, Tom

I never thought of that(they crank the heat up), if I put a new system there will cost me a fortune, I can just run a pipe from my water cylinder to their taps, no harm, I just thought if they have their own water cylinder will be better. At moment I have a timer control in my bed room so I can set up the hours I want the system to run, I'm going holidays soon, I am going to move the timer control to the flat till I come back from my holidays. If I could find a way to split the timer control, so we can both turn the system on I will be very happy. I was thinking to divide the bill in 3 parts, I pay 2 and the couple who are living there pay one part.
Thank you very much for your time, really appreciate

This will be a rental and not a place for Granny? How legal is this set up? Are you in the US or out of country? You can rig something up to turn the heat on or off but you can not have a single heating unit serving two units with a thermostat in each unit and if you install a water heater in the flat you'll have to separate the two systems. What I can't figure out is why it was piped like that in the first place. Good luck, Tom

Thanks again for the help, I am living in Ireland, over here we can rent a room in the house so I am covered even though is outside still part of the house.at moment I don't have TRV (thermostatic radiator valve)but I was thinking in get them, so I could if not turn it off, let it running as low as possible while I will be on holidays.