Oh... How I know... Mine are 12, 9, almost 8 and 5. The 12yo is a gem. Older, helps out a lot. The younger three.... When they start acting up and are grumpy inside, outside, wherever they may be, I send them all to bed. No talking. No playing. Just go to bed and stay there til I say you can get up. About 10-15 minutes later, I let them up on one condition: get along or you're going to go back to bed.
Sometimes it's not always us who needs a "time-out" and time to yourself. Sometimes they need it, too. So we all go to our "separate corners" and come back when we're feeling calmer.