Just went and looked at the pics. Hmm chipboard and drywall, temp beam.
You do have some work to do. If you follow ny plan the beam will have to go, which can be replaced with a stud directly under each rafter.
Back to my plan
Lift up the other end of one of them just by hand has high as you can and support it with a 2x6 a few inches to long at about 12 ft from the back wall.
You want to have it at an angle so when you tap the bottom in it will lift the rafter, but not yet.
Lift each of the new rafters and place a 2x6 under each. 2x6 want to be the same length and placed in the same place on each rafter.
If we lift it like this the rafters will roll over so to hold them up right each pair will want 2x6 blocks on edge between them measure at the lower wall the distance between each pair and hopefully
the guy that sheeted the roof kept the layout straight, if not you may have to deal with that as you lift.
You want blocking near the bottom and close to where the support 2x6s are.
Thing slipping is always a concern so I would use hanger straps to attach the bottom end of the rafter to the wall and to attach the support 2x6s to the rafter
Now you should be able to lift them into place by tapping the bottom of the support 2x6 in. I would be using a 10 pound hammer for tapping each just a little at a time,working back and forth.
You may find that they have slipped up the roof a little when you have them in place, you may be able to hammer them back down with a big hammer.
I have said back wall thru out that may also mean front wall.
You will want to watch carefully that everything is staying straight as you lift extra blocking and bracing may be required.
I didn't suggest lift it straight up because iI was thinking you could lift the rafters off the back wall.
You may want to lay lumber on the floor under the support 2x6s to spread the load over a greater area.
I have not done this before, I have repaired 2 with a simular system