I understand the outside crack completely; the inside one, I can't tell exactly where it is (to understand why it happened), but in looking at it, I think you should treat both of them as "serious" cracks and repair them as such.
I would repair both of them from the inside, if you have access.
Okay, for now I'm not going to elaborate on every step, but I will give you the general idea; if you do go ahead with it yourself, we can always get down to details.
Essentially, you need to grind/sand the inside out around the entire crack into sort of an big oval. You would want the sanded area to extend out, oh, say 2-3" on each side and each end past the crack. (More is fine too; but not less.)
Once you have everything prepped, you make a pattern of that whole area and lay it on top of some fiberglass cloth. I would use biaxmat 1708, 1508 (or similar) because it is structurally strong. You shouldn't need wood, holes at the end of the crack, or anything else given that this is not a cored structure to begin with. The repair will be many times stronger than the original construction.
You then cut 2 or 3 pieces of cloth, with one full sized and the rest staggered a bit smaller. Then you wet out the shell with neat epoxy resin, and then wet out the cloth on your plastic work bench. If you want, you can stack the patches right there and then transfer them en masse to the wall.. Place the patches on the wall with the largest one against the wall and the smallest one towards you, then squeegee the excess resin out, and let it cure. If it wants to "flop," you can use some strips of blue tape to hold it in place.
If you have insulation, etc. on the inside, you will not need to fair the repair; if the walls are "bare painted," then you will want to fair (I'll leave that out for now).
On the outside you would clean out the crack (after the inside is repaired) and then fill with fairing compound (depending on how large/deep the wound and then gelcoat. Of course you can ignore this on the one that does not extend to the outside.
Now, as to what caused it, at least on the one near the door I would say either weight
on the roof (A/C/, snow load, etc.) or possibly a cracked frame (sag). Although the repair will be many times stronger than the original shell, it would be good to make sure the force that broke it is no longer there.
To effect these repairs, you will need to have supplies on hand. A partial list would be as follows:
Epoxy resin and hardener
wet-out surface (plastic, paint
squeegees, disposable brushes
nitrile disposable gloves
acetone/vinegar/or denatured alcohol
respirator, goggles, hearing protection
Tape, newspaper, plastic sheeting, etc.
mixing cups for epoxy
tyvek suit or junk clothes
This gives you the basic idea, anyway. Feel free to ask questions if you decide to go ahead with it. It's not that hard once you have the supplies on hand. But, like cooking stir fry, you do want to have everything laid out and ready to go.