If your leopard sailfin is a gibby (so many common names for the same fish sometimes!), then there's no chance of it breeding in an aquarium, even less so with a different species - so I wouldn't worry. I've not heard of a feather tailed plec (I've heard of a feather fin synodontis though) any pics?
Here's info about your gibby (if it is one):
http/www.planetcatfish.com/catelog/speci...?species_id=148
If that's not your fish, post some pics and we'll see if we can id it for you
Edited to add - if it is a gibby, you're going to need a tank at least (bare min) 5 x 2 x 2ft
When did you buy the feathertailed plec - as your previous posts say you only had the one plec?