do the cat sharks look like this:
http://www.****************/images_01/white_tip_02.jpg
if these are the fish you got, which is very common at the fish stores, they will do fine but have different needs as they mature in which the pleco will not. I can't say abou the ghost knife as to which environment he will need. The cats though will eventually need to be weaned into a brackish environment of which the pleco will be intolerant to as they are salt sensitive. They may be able to withstand the salt for a short time but long term is never good for them.