Your local community health system might have a behaviour support unit you can contact for some support. When my
DH first started working OS, my DD1 (then 8 yo) started kicking up bigtime, so I asked for help. A really lovely kind lady came to our house, observed the dynamics, and gave me some secret mummy strategies for coping. Basically it's all about making the consequences fall back on them, but also creating positive family time that they want as a reward. This might mean 1/2 hour of special time before they go to bed, playing a game, reading a book with mum and/or dad (tv doesn't count
LOL). Then each night, the amount of time they muck around after bedtime gets deducted from the next night's bedtime, and they miss out on family time. Eg, if they usually go to bed at 8.00 and they muck up for an hour, then the next night's bedtime becomes 7.00pm. Trust me this works like a charm. Also you could try to stagger their bed times so one goes to bed half an hour before the next one. Anyway that's just one trick they taught me, of many.
HTH