Oh thats awesome you have a relative like that! Monster Clay is a great clay, holds a stupid amount of detail X3 but if you want to keep it you have to make a mold of it (oil based=never dries)
You can mix super sculpey and sculpey firm to make it more stable- I do understand the frustration with it.
Air dry clay is the best XDD The kind I use doesn't have that marshmallow-y feel that more children friendly has. I also like using apoxie sculpt on it for any fine detailed areas.
my favorite to use is this kind: