In-law frustrations!

So my daughter is turning 5 and her grandparents on dads side were planning to come for a small family party and stay late so we could go on a date. Well after 2 weeks of planning they just tell us they are canceling and could we do the party in a few weeks?! I am so pissed I can’t even see straight. Every time they make plans with us they cancel and my baby girl is the one getting hurt. Now we have all this party stuff and no one to be at her party, she’s not in daycare or preschool so how do I give her a party when don’t know anybody?