You need to assume that he WILL be EXTREMELY vindictive and plan for that, at the same time as hoping for the best.
This is the man who has been cheating on you and stealing money from you for years . He’s not going to be reasonable and hand over half of the matrimonial assets, he will fight for everything.
I see the attraction of the plan to drop off his car and his keys. But personally I’d not do it - too much potential for unpleasant drama.
Id just let him come home on Saturday and say that he’s leaving and go “ ok “ with zero reaction, as if he told you that he’s popping out to the supermarket. Just ask him what his plans are to have the children stay with him 50:50.
That will upset him and his mistress far more than drama from you - the thought of the kids with him half the week.
Men like him thrive on the “ my wife is a psycho, that’s why I’m leaving her “ story. The keys through the door thing just proves to the OW that you are crazy and he can fall into her loving arms.
instead you can to send him polite emails asking what part of the week he wants the kids ( which I’m guessing isn’t part of his dream with OW).
He’s going to send you emails back saying that he DOESNT WANT the kids half the time, no doubt dressed up as it’s not being in their best interest, they need stability etc .
Then if you ask for his plans for the children when he’s in UAE - he’s just going to mutter something about seeing them in the holidays . You wont have to fight for sole residence - he will give it to you.
When the kids are older , you can show them how you tried to get their dad to stay in contact with them and he chose to walk away. Otherwise you will get the blame for his choices.