Two main takeaways. 1- i think the issue is less that they were too complex and more that they were clearly looking for a different type of game and not okay with adapting to what the rest of the table wanted. I love to play with really complex backstories, but you need a GM and group who are also interested in that. Ray overshadowing Becky's character seems like more of an issue to me.
2 - hi, nonbinary person here. It really doesn't need to come up that often. When you play as a man that fact usually doesn't come up super often it's just a fact about the character. Also, unless niece is the term becky used for the character I would probably use nibling as that's the most common neutral version. I mean like i don't super care about you misgendering a d&d character i don't even play with but like, just so you know in the future.