It isn't easy with those ages.
Sounds as if there is no break if one is waking at night and the other is awake at 5.30. You are running on a near empty tank. Sounds as if you are doing it alone too.
Do you have any family that could help this week. If only to have one if them for a short while- especially if they are winding each other up.
Summer may be easier if you can plan ahead a little and put some support in place. Don't think about it this week ( you are doing more than you can cope with anyway) but start some research soon.
Do you have any mum friends, with children of similar ages. Trips out for walks, to the park, for a picnic etc are easier with another adult. If the older one wants to go at a faster pace than the younger one can manage, two adults means one could go with the older ones for, and one with the younger ones, then catch up and swap over if you need to. Also means the little ones have someone the same age to play with, which they will probably be happy with.
Are there any children's activities provided by your local leisure provider/council etc in the school holidays. Summer info may not be there, but iworth looking now, because there may be something this week you can do.
For us the local leisure provider ( was part of the council but now is a separate company - still really council controlled) offer children's activities all year, plus extra in the summer. The listing currently shows the half term activities, but will update to summer in a few weeks.
Some activities are free, others you pay for. Some you book, others you don't. There are pre school activities too.
Places such as libraries have events on during the holidays which includes little ones.
Sometimes there is information given out by schools etc about what is on. Assuming the 4 year old will be starting school in September, if not already in a nursery attached to a school, can you look at newsletters on the school website at newsletters for any info of summer activities.