As long as the homemade ceramics do not contain any metals then it's safe to microwave the homemade ceramics.
It also depends on the glazes used.
The pottery for the homemade ceramics will be fine in the microwave but some glazes have a high metal content and will get very hot or, at worst, arc in the same way that a metal item does in the microwave.
So you need to know which type of glaze was used in the homemade ceramics.
As long as the homemade ceramics does not contain any metal content the homemade ceramic will be safe in the microwave.
I've made homemade ceramic mugs through pottery and the glaze I used was not metal content glaze so it was safe to microwave and I've microwaved my homemade ceramic mugs and they have been just fine.