jnyusa--
hey, prim was right!
all--
Seneschal and castellan are too feudal norman french for Tolkien.
Collectively the closest Old English would be the
Witangemot...individually, apart from
thegn (the Anglo-Saxon spelling variant), options would be
ealdorman or
eorl...both of which are landed titles, if it matters to people;
runwita, sort of a counselor;
raedbora, similar;
hyrde, more guardian or keeper, plural
hyrð.
Myself I like the idea of keeping
Master and
Thegn for Mayor alternates/deputies/whatevers. How about Rangers, in its "original" sense?