Engagement Party Guest List

We postponed our engagement party so we could do it outside. Do we only invite people who are getting an invitation to the wedding or do we invite all of our friends and acquaintances? Little backstory, every year we hold a giant party in the summer for FH's birthday with friends, friends of our siblings and our kids' friends. Everyone is welcome. Since we will not be holding one this year and we have limited space on our wedding guest list I thought we could just hold it in the spring as a celebration of our engagement. My only worry is that people may get upset they were invited to the party and not the wedding. Note: we are not asking for gifts.