Capitalising the word "member"

Hi

I'd to please have some clarification about an issue I'm having at the moment - I am part of a club in my town, and have recently started helping out with their social media materials. The problem I'm having is they're insisting that the words "member" or "members" should be capitalised in all materials ie. "There were many Members at the function last month". I've tried to explain that it shouldn't be capitalised but to no avail. If someone could possibly explain it in a simple manner so that I may then show it to the other people involved in the social media materials I would really appreciate it.

Thanks!