Both the shattering, and the lack of adhesion are signs of old decals. Decals do have a shelf life. Old decals are a problem not just with Guillows, but anyone's kit depending on the dealer you bought it from or how long it has been in your stash. You now need to contact Estes, or whoever now owns Guillows and get a new set.
Whenever I start a build now, I scan the decal sheet with a scanner hooked to my computer. That way, if the decals are bad, and no other fix method works, I may be able to make new ones on inkjet decal paper.
Next, I try a decal from the sheet that I will not need for the model. It may be a decal for an option I am not using. Or, many decal sheets have brand and kit identification numbers, that are actually decals too, but not used for the build. I try to apply one of these to a piece of scrap. If it shatters, I coat the whole decal sheet with decal film. Micro Scale makes a very good decal film.
If adhesion is a problem, it can often be fixed by applying a diluted white glue/water mix, about 1:1 to the back of the decal.