Well, the dominant male is a nice shade of blue...but females are rather plain.
L. Wiliamsi get to a max of about 3 inches... a full grown ciliatus is usually 8 inches... almost 3 times the size. You can bet the crestie will try and eat them when they cross paths, especially if the size difference is dramatic like a young williamsi vs. a fully grown crestie.
Another consideration is the environment requirements...they are close but they are a bit on the high side fro a crested gecko. You'll also need UV since wiliamsii are diurnal.
Another thought is if you put a breeding pair, any hatchlings would be food for sure.
Here is a thought...if you want something else in that tank consider the following:
1. Giant Millipede (NOT centipede)
2. a glass divider to separate the species
3. Doing something on a scale like
this, where a low mix could work.