I was going to suggest Capt Tolley’s Spider Crack stuff. I have used it on spider cracks on the upper side of my boats and a couple of times on the deck when I got to them early. It is colorless and years later the crack hasn’t altered or budged. But I am guessing the second photo is what you are calling spider cracks. It may appear worse in the picture than it is from standing next to the boat, but what I am seeing there is beyond what I would trust long term to Capt Tolley’s.
But weather is improving and that is likely to turn into a lot of gel coat replace and sanding - so maybe you don’t want to take it on right now. The loss of gel coat along the keel, particularly the bow where you will likely hit things, and adding something like an EZ keel strip may be a higher priority.
If this was early June and I was just three weeks away from loading up boats to go to Maine, personally I would handle what you are calling spider cracks with Captain Tolley’s reinforced with tenacious tape over the area. Knowing full well that when all comes off, you are looking at the full gel coat job. But the combo of those two would hold things together until sometime in late September when it might be a better time to have the boat out of commission for a bit.