You could use BuddyPress’ x-profile fields to create a required, custom radio button for gender.
The hard part will be hacking the activity feed to show the pronoun differential.
You’d have to create your own function similar to Buddypress’ bp_your_or_their() function.
Then apply that function as a filter on bp_activity_content_filter.
That is what I was thinking, I already created the x-profile field, I just wasn’t sure which way to go with it, or if someone had already done something similar, therefore making it easier for me haha. Thanks.