Welcome to the forum!!!
No u dnt need to add an s ' the end of Salaam...it is a word that stays the same for one person and more than one person...there is no need to make it plural.. If you have any other questions 'treth betold' ask away...we will be more than happy to answer or at least say what we think (if the questions don't have a simple, clear answer) Hope u enjoy your time here...
Wasallam alaykum