Hello Souvik !

There are many factors that are responsible for a compound to be soluble in water , like Nature of compound : Ionic or Covalent , Hydration energy of compound , Lattice Energy of compound.

And , above give Compounds are fluorides of Alkaline earth metals. Now , as iconic bond strength increases as we go down the group , as a result lattice energy also increases and hence Solubility decreases .

Hence , MgF2 is more soluble than CaF2

Hope it helps  !