Confusion in comparing melting point
You can get an estimate of the bond strength by using Coulomb's law and periodic trends for atomic radius. $$F = k{ {q_1q_2} \over r^2}$$The charge of all these alkali metals is the same in these compounds, so the only difference in bond strength comes from the the distance between the charges. The distance between the charges is related to each atoms' atomic radius and that is an increasing trend as you move down the alkali metals. 

So, if distance is increasing, the force holding the solid together is decreasing, which would justify the trend $\ce{LiH}&gt;\ce{NaH} &gt;\ce{KH}&gt; \ce{CsH}$ for melting point.