I think Pusses is the informal plural of Puss. Like don't be a puss vs what a bunch of pusses.
Pussies would be the plural of Pussy. LIke my gal is freak and has two pussies.
When using it in the slang form of referring to people as wusses you can either call them pusses or pussies.
/grammer lesson you won't learn in grade school.
this made me laugh, thank you