Aw I'm sorry you've injured your knee that sounds awful, and it's SO impacting to have a physical injury when you're caring for twins.
I slipped 2 discs last year, so badly thay I was hospitalised for 2 days. The recovery at home was slow but it would have been much quicker if I didn't have giant twins to look after. (One was 23kg at the time and still needed picking up / lifting a lot due to their special needs).
I'm all better now thank goodness.
I hope you can get help and time to recover your knee.
May I suggest approaching HomeStart to ask for a volunteer? They might be able to give you the break you need and deserve. One of Homestart's criteria / aims is supporting parents of multiples. Here's a link:
https://www.home-start.org.uk/twins-triplets-and-many-children
I should say, I applied to have a volunteer for this myself, not so long ago, but sadly since I live in a very populated area of London, they couldn't even put me on the waiting list due to huge volume of need where I live! So that was a bummer but hey ho.
Its worth having a look and approaching your local branch if there is one. I've heard really nice things.
I think I might volunteer for this charity when the kids are older. If I'm still physically functioning. 🫠
Wishing you all the best with your little ones you sound like a lovely mum.x