"So when the jack post just falls thru the floor or breaks a floor joist, do you just stand there with a dumb grin on your face."
You could put another jack in the basement bellow it. On second though i don't think it would need that much pressure. I think simple adding the some 2x4" trusses and using pry bar you could correct the sagging roof beam a bit, it looks like only 1". I'm assuming the rest of the structure is solid. Wood has memory it shouldn't be that hard to get it to remember.
"The two samples of trusses you posted are designed for certain loads. How about you explain the difference and which one is used for what."
If you add more structure but don't add more load what could go wrong? The trusses are ment to hold the roof up. Maybe the old roofing was too heavy?
I don't trust engineers so much,