You are thinking too much as a whole so break it down, plan it week by week and then you only have a small section to go through.
Find activities that will get you out of the house and tire them out, plan things they can play alone to get some rest and make sure you use screen time to your advantage (possibly look into getting Disney plus for the summer if not already, as putting on a film for the witching 5-7 hour is great!)
If you have the money then most schools or clubs run a holiday club so the 5 year old could attend, alternatively you could get an intensive swimming course or something they go to each day.
If money is more of an issue then you will have to get creative but the churches near us have loads of activities for next to nothing!
A general week could be as follows
Monday AM - Local Parks and a picnic lunch
Monday PM - Craft activities, more structured if you wanted like a set or painting the letter of their name and sticking stickers on etc
Tuesday AM - Making a den/shop in the house/garden
Tuesday PM - Make a cinema sign, design popcorn boxes and then have a movie afternoon with homemade popcorn
Wednesday AM - PJ morning play with their toys
Wednesday PM - play date at the park with another family, or splash pad if you have one near
Thursday AM - soft play
Thursday PM - get soft toys down to set up a tea party. Encourage menus with stickers
Friday AM - Go swimming or paddling pool out, use brushes to paint the fence with water
Friday PM - designing digestive biscuits with icing, sweets and chocolate buttons. Eat watching bluey
then you can do the weekend easy and there’s only 5 weeks left!
You can plan days to town, see if there’s any woods or trails nearby, go on a bigger outing on the train or visiting family. Planning stuff is the way to go