How would you feel in this situation?

My son's 5th birthday is coming up next month on the 16th. I have been planning a family party for him since January and have talked about it several times with my family members, letting them know the date (the 18th) and the details. My dad, stepmom and 2 of my siblings live around us. My mom and brother live in another state 15 hours away. My sister is in the military halfway across the country. So my sister was planning on coming for his birthday and as an added bonus her birthday is on the 19th. My mom is driving up with my brother since they live in the same area. Off and on my sister has said nothing was set in stone because she is in the army and can be deployed at any time. I let everyone know this. Meanwhile my brother has told me my dad was planning on visiting him sometime in April. Ok, whatever. My younger brother up here also said he had plans for a trip sometime in April. Dates were never mentioned. A week ago my sister said she was definately coming up. A couple days later she called me back and said she was getting deployed and can't come. So I let everyone know the bad news. Yesterday I was visiting with my dad when he told me I ruined his vacation plans by telling my brother that my sister was coming up and so he was coming up and that is when my dad was going to visit him. Umm, why would you go visit him on your grandson's 5th birthday?? Then my younger brother also tells me his vacation plans happened to fall on that same week. wtf??? I've been telling people forever about this and now they drop it on me that they'll all be gone for his birthday? It's like they don't even care. Plus my dad implied that the only reason my brother was coming up was to see my sister, not even for my son's birthday. He has to come up now because he's my mom's ride. She seems like the only one even interested in his birthday. I feel really hurt about it all and I'm not sure if I'm overreacting...