The Snow Spider= Y Corryn Eira (I thought corryn sounded better that cop, the other option in the dictionary)
The spider is silver coloured and magic.
Emlyn's Moon= Y Lleuad Emlyn (is lloer more poetic/regional? I've usually seen lleuad in real life, but the dictionary offered me lloer too)
The title refers to both the real moon, and the name of a place, Perllan yr hanner Lleuad, so I went with Lleuad to match it.
The Chestnut Soldier= Y Milwr Castan
The third one is giving me trouble. The title also refers to the colour of the soldier's hair, but castan only seems to refer to the nuts in Welsh as far as I can see, not a colour, and I need to keep the chestnut in.