OP I hear you. And I only have two (1 ND) so big kudos to you!
Some things we find helpful -
The children know that they must do the following before ANY screens:
wash, dress, breakfast
tidy room and make bed.
Exercise - walk or park with dog ( and me) or dancing or whatever.
read something or listen to audio book
something arty or crafty - even if it’s just colouring a picture.
minimum 1 chore ( not including their own beds which is a given)
One game , usually uno.
They are each responsible for planning, shopping and cooking one meal a week - obvs with adult input and assistance. They love this!
All of these must be completed before screens. The children end up competing to see who can complete tasks quicker! After that, all bets are off and screens are fine.
Food - they are so much better if they eat healthily! Too much sugar results in being hyper followed by a meltdown. That may be just my kids though.
At the beginning of the summer, we sit together and list ideas and plans for the hols. Generally free or cheap - park, beach, woods (all with picnics), museums, library, movie day or night, swimming, outside fire etc etc. We usually holiday every other year, first time this year since 2019. No big treat days out if holidaying - maybe 1 or 2 if not.
The list gives them some ownership and they enjoy ticking them off.
I hope some of that’s useful.