We are doing a mix of live teaching and set work. Replanning lessons for home learning is a lot of work. We generally have to cut down lesson content, rewrite explanations, remodel tasks, and find supporting content e.g. videos. For Y11, I record explanations every other lesson, for Y10 I am trying to do this for 1 in 3 lessons.
Feedback is also a lot more time consuming, as is helping individual students with technical or other problems.
We also have to contact/chase up our tutees who aren't submitting work, and this takes up a huge amount of my time!
I do all of this alongside 5 hours of live lessons a week, one day in school a week and a live tutor time every day- so I would say it would be doable for teachers at your school to come in.
HOWEVER, having all teachers in on a rota is actually riskier, IMO, because you are having more adults in the building, more adults interacting with the same children and more chance of someone bringing an infection in. Those teachers may also then need to send their own children into school, increasing the risk to someone else. If it's possible to minimise staff coming in, and everyone can do their jobs, then I think this is the safest route on a school population level.
If you feel individually unsafe- e.g. because the group you are supervising is large and unable to distance, that is a separate issue, which I definitely would take up with your line manager and union.
And the solution might be to get teachers in to decrease group size- but that has to be balanced against the risk of having more adults in the building.