I think you’re sensing that you’re losing control of your own home. I think you’re right. This is a bit of a threshold moment. Be calm, hold firm, avoid details, refuse to argue. ‘It’s not working!’ should be enough.
Sit them down and calmly report it’s time for them to make new arrangements, urgently. Then explain you’re just trying to avoid a relationship ending screaming match, and the long hard feelings that will surely follow, ‘Let’s be mature adults about this.’
When they ask, simple say you’ve tried your best, you’re certain that they have made their very best efforts as well, and you appreciate that sincerely. But as things are, nothing is changing and what IS, cannot be sustained. The wise move it to end it now, before we destroy our family.
We’re sorry, we thought we could help, we thought you’d be happy, and that we could all cooperate. Perhaps we expected too much. If so, we offer our sincere regrets for that.
As adults, you all need to accept that, for all our asking, suggesting, pleading, we have not been able to move forward to anything we find comfortable or sustainable. As you have assured us, this is all you can do, and as we can see you won’t change things, we are left only to return our living arrangements to when it was manageable for us.
We appreciate that everyone made a sincere effort and gave it their best try, we know we did. We now need to maturely recognize when something isn’t working, and brave enough to make the needed change, to keep our home and mental health afloat.
We ask you to take some time to think about our words for a day before responding. Let’s talk again then. (Don’t re engage, no matter what they jump into!) repeat, ‘we’ll talk again tomorrow.’ Not before.
You find yourself in pretty deep here. If they use ‘the children going into care’ thing like a sword, and you cave, the rest is moot.
Good Luck!