Why is the melting point of BaCl2 > BeCl2 while CsCl<NaCl
Sodium chloride and caesium chloride are both primarily ionic compounds. Within ionic compounds, a greater melting point can be caused by a higher ionic charge or a higher charge density/better interaction. Since both have the same charge while sodium has a smaller ionic radius, the sodium-based crystal is held together better due to more interaction than the caesium based one.

When comparing barium chloride and beryllium chloride, you are essentially comparing apples and oranges since beryllium chloride is a primarily molecular compound. In its gas phase, it forms $\ce{BeCl2}$ monomers and $\ce{Be2Cl4}$ dimers. The intramolecular attractions in molecular compounds are typically rather strong with the intermolecular ones are weaker. For ionic compounds such as barium chloride, we cannot distinguish between the two since we cannot define molecular entities.

When comparing ionic compounds to molecules, the ionic compounds typically have a much higher melting point (with exceptions; both low-melting ionic compounds and high-melting molecular compounds).