Hey there!
Thanks for the feedback! We really appreciate that you like the characters we made. While MANY of the characters are Poly, there are a few we couldn't see romantically sharing in quite that way (though none will object to you continuing to see others for fun). You can find the guide to which fall into what category here: https://sinspirational.com/paradise/walkthrough.html if it helps make a list of those you'd like in a more 'big family' method. (Its about halfway down the page)
Unfortunately, development has ended on Paradise as we move on to our next project, and that one would not be small. There are several parts in the game where your romantic partners will show up, so it would be several months of work to add in all remaining characters to those lists. But I do hope you keep an eye on us for further games and romances!