True.  I'm thinking more along the lines of recreational use, rather than legitimate use.

OP is alleging that Dad is a drug dealer with a rap sheet, and OP is complaining that 3 nail drug tests for Mom are an unreasonable demand, without stating why.  So I'm inclined to think that Mom and Dad share some hobbies or have some related/complementary hobbies.

But perhaps that is just me reading between different lines.