I have a 2 year old ferret and a 6 month old I been trying to get them to get along but the younger ferret, always licks and nips the older ferret. My older ferret hisses at him and sometimes yelps its not a really loud yelp but I can tell she doesnt like it. I need to know if I should let it go on or just keep them in seperate cages I cant tell if my older ferret Izzy id just annoyed by my younger ferret or if hes hurting her. How can I know?

     Sorry if this doesnt make sense I been up all day doing finals.