Can I use the site pet images of two colored devil's spawn rabbit and snowy owl in Lillian and Claire's encyclopedia?

Also, more of a lore question: Do pregnant wizard mothers have things to tell what gender the baby is, or is the baby always a surprise?

I believe most of the images used for the informational parts of the site can be used by the public, so yes.

There isn't much canon lore on wizarding pregnancies, nor do we have any official written lore on site, but historically there have always been methods for humans to predict the gender of a fetus- although the legitimacy outside of modern methods have always been questionable. It wouldn't be too out-there to say wizards use these old methods, but put their own magical spin on them with herbs, divination, or potions and whatnot.