I noticed that all these words have the same ending: mother, father, brother, other and another. Does anyone know what the suffix -ther means? Or is it a compound suffix: -th &-er? Thank you
It is possible (but not certain) that father, mother and brother share a suffix: compare Latin pater, mater and frater. I don't know that anybody has a convincing answer for what this suffix may mean - or more to the point, what the roots without the suffix might mean.
Other and another, though, do share a suffix meaning "one of two", also seen in English in "either/neither", "whether", but also in Latin alter ("one or other of two") and neuter ("neither"), in Greek heteros ("different") and in Russian vtoroy ("second").