So my brain bubble for a religion in my world is basically that the gods consist of three beings: God of light, God of dark, and Goddess of in between/magic. If anyone's got any brain bubbles on how I could further expand this, names for said deities, holidays and ceremonies, etc. that would be great.
that actually sounds like a really cool brain bubble. some brain bubbles for names, just use latin, greek or gaelic wods, i find they sound really schmancy haha. or another thing i am brain brewing of doing is taking gods and goddesses from loads of different religions, changing them a little and making something else out of the whole group of things. it sounds wonky-donky but when done properly can be really cool
Consider using the calender/orbit party to figure out when the hottest/brightest time and coldest/darkest time of the orbit party is. These could be used as holidays for the light/dark gods and then the halfway points could be holidays of the goddess. For names I would think about:
Bryn, Brynnyg, etc. for the god of light
Shendar, Shen, etc. for the god of darkness
Khura, Khuri, etc. for the goddess of magic
They just seem like they fit.
For ceremonies you might have priests/priestesses doing a ceremony at each of the above holidays to turn the seasons, say good bye to one god and welcome in the other (or have them fight each other like the Oak King and Holly King), and honour the balance at those points.
Hope this helps!