I have triplets (9) and twins (4). Trips are playing Tennessee tourneys and have under 10 rankings. Twins already know what strokes are, who the pros are, constantly bug me (in a good cute way) to play, and imitate the trips when we go out to play on local courts. Five kids on a court is pretty interesting. If the twins behave we give them a ten minute "baby intermission" and do relay races. Imitation is a powerful learning tool, absolutely amazing the stuff they pick up. I am primary coach for everyone. Luckily I am a former teaching pro and love working with my kids. I could simply not afford to develop players anyway else! We play about 6 hours a week winter for big kids, plus lots of ping pong, and volley work. Little guys play about 10-15 mins. a day and I always leave them wanting more. Summer big kids play about 15 hours a week. We belong to affordable club and there are some good kids to practice with and play matches.
Good luck on the journey. I am right there with you.
I wish there was a book out on how to be successful coaching your own kids...