Help me nut out this energy saving conundrum!

We are currently living in a very old (approx 90 years) and very small uninsulated residence.

We have two heaters that work alright but they aren't located in the best places for our living arrangement. One is a split system that is located in the bedroom we put the kids in (yes 4 kids in one room lol) and the other is a gas heater in the kitchen.

If I have the split system on all day, the house will be a comfortable temperature in the evening as the warm air will end up through the house. Our "issue" is that DH insists that the curtain in the kids bedroom has to be closed to stop the warm from escaping. He is obsessed with that.
Little Miss R likes to play in the bedroom, but not in the dark so the light is on most of the day. It bugs me to have the light on because the curtains closed during the day.

I'm sure you can imagine the arguing we've had about this lol so what is your opinion on which option is the more economical option?
Curtains closed/lights on/heater on or curtains open/lights off/heater on.

Don't dare say heater off because we tried that and it's not an option unless we sit in bed all day. Yes it's that cold!

Does the sun shine into the room at any point? Because if the sun is shining in it will be heating the room so you could have a curtains open sometimes regime.

Not this time of year. In the height of summer it got a bit of sun but it's a SW facing window, so with the shorter sun path in winter it doesn't happen.

For a standard light fitting (batton holder centre of the room), you'd be better off economically to have the curtains closed and light on. If it's multiple downlights, then economically the curtains are better off open.

Personally your probably usine more energy and not making a huge amount of difference by having the curtains closed & the light on.
Your probably better off having the curtains open and saving on electricity by having the lights on.

Even if you just open the curtains during 'play times' and shut them again when the room is not being used?