How can you get invited in the Pixar animation studios if you don't have a family member or a friend that works there?

Maybe see if you can find somebody that works there on Couchsurfing or LinkedIn. If you're very sincere and have a good reason, who knows, maybe they'll help out.

We got in through a special event hosted for CSSSA to see Coco. They seem to do a lot of special events fundraisers but they're not listed anywhere I can find.

Based on my knowledge, there are no studio tours that you can pay for and Pixar is not open for the public. However, I was able to enter Pixar through an organization that held an event there, allowing me to see the free screening of Cars 3. In other words, it can be quite difficult to get in based on my experience.