[jmarjorie]

Would anyone know what are the ideal widely available and cheap inorganic compounds to double decompose CaSO4 and MgSO4 into their more water soluble counterparts.
Please note that the sulfates of Calcium and Magnesium themselves are insoluble in water. The other inorganic compounds and their Sulfates have to be soluble in water. Any such compounds ?

[AWK]

Both, CaSO4 and MgSO4 are soluble in water, though CaSO4 sparingly(~2g /L, MgSO4 more than 100 g/L at RT). CaSO4 is soluble in concentrated solution of (NH4)2SO4.
OFf course, you can obtain other calcium salt, eg. through sequence CaCO3 => CaCl2