My 2dc are a little older than yours and I'm a teacher.
The last thing I would want to do is to look after a 9 and 11 year old as well.
The holidays for me are 1. time to relax and do nothing and 2. time to indulge my dc in interests we have not had time for during the busy terms.
Thirdly we also make time for the usual holiday activities as all families do (days out, go on holiday).
Teaching is a very unique profession as term time is so busy and structured, so some school holiday time needs to be spent decompressing. And also some time will be spent on planning for the following term. We also have no flexibility in choosing when to take leave.
When you have school aged dc you need to plan you your own needs and theirs.
I would be making plans for the coming summer holidays now if I was in your situation.
Organise time for all 6 of you to go away. A proper family holiday where everyone is included.
Then plan time for you and your 2 dc to relax together at home alone.
And then plan to take your dc away for some alone time just the 3 of you. Your dh can sort childcare and also spend quality time with just the two of them also.
I would not become the default child care for them (and him) for 50% of the school holidays!