They are not "easy" to fix as you are talking about cosmetics, but can be fixed by a good gel coat guy. The real problem is that fixing the cracks does nothing to fix the problem that causes them to crack in the first place. Until you do that, there is no point in trying to fix them.
You have to put in the structure to prevent flexing that the mfg did not. That means adding bulkheads/bracing, or whatever is missing that allows the skin to flex in the first place. Sometimes there is just not enough boat there to truly fix this. Especially when the skin itself is too thin to stabilize without adding additional layup.
As far as how..., you have to open them up to remove all the fractured gel, and also to create a large enough area to "key" new gel in using a mechanical bond. That basically means a V shape. A can opener is almost ideal for this (the old metal kind, not one of those things with a crank...P) Then you fill with new gel coat. Finally, you sand the entire area and spray a surface coat of gel that you color match individually to the particular area you are fixing (different sides of the boat will have different colors due to sun and fading). Lastly you then finish sand though all grits and finally cut/polish using a buffer. This is a lot of work with quite a bit of art to making gel colors blend in. You won't be pleased if it simply cracks again after you do all this work within a few days or months of doing the repair.
