Tear it all off and rebuild a roof that's not made out of 2x4's.
To fix-at-it, tear off all the ceiling drywall. Temporarily support the beams and remove the sisters (the tacked-on LVL's). Insert new 2x4 sisters that go the entire span, tucked above the header that would of been behind you while taking that picture, short enough to slip up into the cavity, just short of sitting on the existing header above the window.
Keep them as big as possible while still being able to psychically insert them. A slight angle cut on the bottom of the 2x4 where it will sit on the header behind you helps squeeze it in there. A slice off the side might help get the other end up into the cavity as you will be trying to angle them in there.
Then attach a new header to the face of the old window's header, ideally the entire length of the room, across the top of the windows; a cripple for your new joists. (yes it will show and stick out into the room a little, just pretend its a decorative trim, perhaps bevel it or route the edge)
A framing nail gun may split the existing joists, you might want to use deck screws for attaching the new sisters to the existing joists. Stagger the spacing on the fasteners; one high, one low, ect., every 8-12 inches.
Fix the roofing before you do anything else.