The correct order of solubility in water  $\mathrm{CsF}>\mathrm{CsCl}>\mathrm{CsBr}>\mathrm{CsI}$

As the difference in the size of cation and monoanion decreases, solubility decreases. In other words, if H.E. decreases more than L. E. decreases then, solubility decreases.
L.F. is much less soluble in water because of high lattice enthalpy