I have never understood why anyone counts. It’s the single least effective disciple method I’ve ever seen! 
Here is what worked for us (they were hooligans at three and are delightful at ten):
There is little point standing at the door to a room shouting/repeating/being ignored. You’ll just end up stressed and with a headache.
Crouch down to their eye level, make eye contact with each child.
Touch them to make sure they are looking at you.
Low firm voice. Not shouting, not angry but you have to sound like you mean it. (You do have to mean it)
I’m a big believer in giving at advance notice of things. We are leaving in ten minutes, screens off, shoes and loo right now.
If screens don’t go off, switch them off. Pick one child and send them
for shoes, send the other to the loo. Make it a race.
Anyone fighting after one warning gets a housework chore to do. Emptying dishwasher. Dusting. Hoovering. Pairing socks. In separate rooms.
If you don’t know who is in the right regarding the toy they are fighting over neither gets it, it goes on a high shelf.
If they are fighting over which tv programme to watch it goes off completely.
If they aren’t great at taking turns buy a timer (or use the cooker timer)
Never threaten anything you aren’t actually prepared to carry out. So if you say “do that again and we’re going home you do actually have to go home instantly if they do it again.
Never give into tantrums. Ever. Teach them that as soon as a tantrum starts any likelihood of getting their own way is gone.
Be clear in different types of “no”. Sometimes we knee jerk “no” but are actually open to negotiation. Sometimes the no is final. Tell them. “I said no and I’m not going to change my mind, don’t ask again”.
Never be frightened to tell that they haven’t behaved to an acceptable standard or have let you down in public. They’re old enough to know and try to do better.
If you need to tell one off remove them from the room their twin is in. It prevents them giving each other positive feedback. Eye level/low form voice.
Remind them just before you go somewhere (a shop, granny’s, a party etc) what kind of behaviour is required. Eg I want to see excellent behaviour today, please and thank yous, taking turns nicely (or whatever)
Praise them lavishly (and individually) for good behaviour. Again I do this at eyelevel, having quietly taken them to the side. I’m so proud of you/that was super behaviour/X’s Mummy said you were a pleasure to have etc etc
Try to spend time one on one. Eg one weeds the garden with Mummy and the other goes to the shop with Daddy or whatever. Separate stories at bedtime.
Finally, get them as much exercise as possible every single day. Long walks/cycling/the park/sports classes etc It really helps.
Good luck 
