Reward them for the behaviours you want to see more of.
Remove or disable the X box. Maybe start by removing it and then they earn it back by a certain number of points for good behaviour.
Also time them on the X box. Make it a privilege instead of a right. Stick to the timer exactly, no excuses.
You don't have to remove the whole thing. Just remove an easy to remove element of it (controller, game, connecting cable) that renders it useless.
Try and have some fun with them. If you are in a cycle of shouting and fighting and trying to demand respect, there's no time or energy for fun and they then grow up too soon and get hardened.
Also try and find some other interest that you can do together. My tech mad 11yo loves making biscuits or cakes and decorating them. Making pizza from scratch also appeals to a lot of kids - making pizza dough is really easy (flour, instant yeast sachet, olive oil basically) and they love arranging their own toppings. To avoid arguments, prepare in advance (get all the stuff together) and don't get too bothered about accidental mess. If they get overexcited, sit them out for 2 minutes and then invite them back in when calmer.
Try reading to them at bed last thing at night. This is a really bonding thing to do. Chapter books which are age appropriate and interesting but not the usual popular nonsense full of illustrations (and nothing where the main character is rude or obnoxious). Something which isn't so "instant" and takes time to build up to so they get a sense of anticipation and patience. Have patience yourself with all of this sort of thing, because if they are not used to it they will probably reject it at first but if you can persevere you'll find they adapt to it.