hin or chin?

[Galin]

It's like the sound in German Bach (as already noted).

CH is only used to represent the sound heard in bach (in German or Welsh), not that in English church. Except at the end of words and before t this sound, was weakened to h in the speech of Gondor, and that change has been recognized in a few names, such as Rohan, Rohirrim. (Imrahil is a Númenorean name.)

Return of the King, Appendix E

hên 'child' hîn 'children', but the plural article triggers a mutation here > i·Chîn 'the children'.