Would you be able to switch off power to the relevant sockets at the fuse box to prevent use of X-boxes etc.?
The shock might make them come to their senses. The quid pro quo for reinstatement of gaming rights would be some help around the house, and not taking you for granted.
(This is a fantasy scenario of mine, when I start feeling like a skivvy in my own home - a common feature of life with teenagers, I think. Haven't actually tried it yet, as my major fault is not carrying through on consequences).
A friend has reclaimed her life by rewarding any rudeness or lack of respect for house rules with a refusal to do anything for the transgressor for the following week - lifts, cooking, washing, ironing etc.
I think contributions would depend on what their incomes were. Are they all in full time education, for example? If they are working, then I think they should definitely be giving you something for their board and lodging.
It's so difficult to stop thinking of them as your children (which they always will be, of course!) and start thinking of them as adults with responsibilities as well as rights.