Japan is not China. They use katakana not Kanji for foreign originated noun such as name.
Ashley would be アシュレー or アシュリー.
Candice would be キャンディス.
If you still really want to get Kanji for those, there are no restriction.
You may try to component some Kanjis of similar pronunciable ones.
亜朱麗 (Asian/American crimson beauty) 阿珠霊 (kid of pearl spirit)
as for Ashley for example. Some more variation are as follows.
A
阿 kid
亜 Asian/American
Shu
珠 pearl
朱 crimson
ley or rii
麗 beauty
霊 spirit
鈴 bell
澪 water trace
Unfortunately, there is no pretty suitable Kanji for Candice as far as I know. Most of candidates are just dirty or plain non-sense only.