MacBook Air, Keyboard, Trackpad

Was there a liquid spill resulting in undetected logic board damage?

Since the machine force boots (and you've replaced all the usual suspect parts) I believe either you've damaged the keyboard ribbon connector, or not completely aligned and inserted the ribbon cable - its a tricky task (track-pad and power button also run through this).

There is a cam lock on that connector it must be unlocked before removal and relocked after. A technique I found useful is to use some blue painters masking tape to create a sort of handle or strap that allows me to lift and guide the ribbon back fully into the connector.

If you've damaged the ribbon cable connector either a computer/small electronics shop (or someone skilled in logic board component repair) must replace it, or, the usual DIY solution would be to replace the damaged logic board.

If this answer is acceptable please remember to return and mark it accepted.