Yes what you’re suggesting is possible, bearing in mind the more layers you use, the room for error increases, so be fastidious when fixing boards.
Wipe any dust away, priming them would help.
Do not allow boards to align, brick bond them, and tape all the joints with a wide scrim and flatten with tile adhesive.
Using latex to feather them is possible, but it is designed to flow, so it would have to be a thicker mix, or use rapid setting tile adhesive.
Use
standard set when laying floor, and prime the boards and any latex or tile adhesive you’ve previously applied.
You could use a PTB adhesive instead of feathering the boards, (pourable thick bed) this would allow you to still achieve a full bed because it would take up any voids.
However these are invariably rapid setting adhesives, they’re messy and quite difficult to use.
You should only mix small amounts if taking this route, otherwise you’ll throw away more than you use.
The task you are taking on is really quite difficult, even some experienced fitters would struggle to achieve good results.
It’ll take time and patience when laying the floor.
I’d suggest starting at the point of lowest clearance at the bi-folds, and working back to the highest.
Coming up from a low point is far easier than the other way around.
In an ideal world you’d have a straight edge long enough to reach from the old floor to the doors, as this is some 5 metres, it won’t be possible, so you should at least use a sting line, this way you can be sure of an even gradient as the floor falls toward the doors.
You will also need an expansion joint between old and new floors to allow for lateral movement.
Put a tile joint on the expansion joint and fill with a colourmatch silicone to match the grout.
How old is the slab, has it been moisture tested?
You’re a brave man.
Good luck.