I think you need to start with some basic tests rather than just changing parts without proving them faulty. I cannot see any mention of a compression test although it has been suggested. (Does not have to be electronic. You must have a compression gauge?).
Spark plugs may give a spark when out of the cylinder but that does not mean there is enough energy to produce a suitable spark under compressed conditions. A spark gap tester is better or ignition primary / secondary tests as already suggested.
If these tests eliminate those basic factors then you can proceed to air leaks / injector signals etc

Steve