Kendall: assuming Kendall is the actual name yu are referring to, "chief of the river glen" doesnt seem that likely to me. The "ken" could indeed be the gaelic for head or chief( "can" "ceann" or something like it in Gaelic labguages, pen in the British branches of the Celtic languages). Dall would be "dale", the Anglo/norse/Danish word for valley. But I would guess Kendall is basically Kendal(modern spelling), the chief town in Westmorland(now Cumbria). The Ken is for the River Kent (the river that drowned 20 Chinese cockle-pickers recently) and the "dal" from dale. basically. Kent valley. The old name was Kirkby(church town) Kentdale.
   now, the etymology of the "kent" I dont know.