OP I feel for you. So much.
Similar experience here for many years, though not quite so intense. ILs usually slept elsewhere but we’re here every single day for months, every year. Also turned up wherever we went as a family, so no escape.
I managed it for years, with escalating tension between me and DH.
Short version of solutions….
Going out, a lot, with kids, who were also fed up with constant presence of ILs cramping our lives. This involved very clear language to show that ILs were not invited - we often met friends to give that a cloak of inoffense.
Consistent absolute freedom for DH to choose to spend the time with his parents instead of with us, with zero judgement or snide. It was always his choice.
Tricky conversations many times with DH to get him to the point of understanding that I and the kids were emotionally cramped by having his parents with us all the time, and that he was not to give them open invitations into our world at all times.
This was the tough bit and involved frank talk of “we are people too, and we are telling you we do not like this and cannot keep accepting it, and your actions are harming and hurting us”
And a couple of full crises along the way that come to mind….
They moved in while mil was poorly, and showed no signs of departing when she was well enough.
Weeks of arguments and despair later, I announced I was moving out to a youth hostel at the weekend to get some space in order to avoid total mental breakdown.
That got through, and he asked them to head back to their accommodation.
And another one where I said he was welcome to go and live them in their accommodation, with kids if he wanted, in order to spend more time with them, but that this is my home, and not theirs, and that I mattered too.
It got easier in a way when I started working from home because it gave a firm reason to keep them out, but even then I had to be really clear with DH that he was not to invite them carte Blanche for dinner every day, or hang out with them in another room of the house all day.
It came to a head when I was ill too, trapped in my own home, persecuted by visits from ILs that I expressly didn’t want and couldn’t do a thing to stop.
Hideous times.
I sympathise, enormously. Truly.
Perfect your and your kids mental well being.