I definitely feel your pain. My DH's family are all useless and we went through this throughout our wedding planning. My two SIL's were supposed to be coming, we booked (and put the deposit down) for their room. We even offered to pay for part of their trip because it was important to my husband that they come. We knew money was tight for them. They repeatedly said they didn't need help, but didn't book plane tickets. Every month they said they were going to do it soon. 2 months before our wedding his older sister tells us she is pregnant and that it isn't safe for her to fly... keep in mind that I'm a doctor. She was going to be 4 months pregnant when we got married. She was not high risk. So we lost the money for their room.
His Aunt and Uncle were going to come, but cancelled their trip because they "couldn't afford it". A month before our wedding they went to Punta Cana for a week. They later told us they weren't coming because they saw it as a family reunion and when his sisters cancelled, they "didn't see the point in coming".
His dad never booked his trip. We had put down his deposit as well and lost the money. We left for Jamaica thinking he wasn't coming. 2 days after we got there the hotel manager told us that they received an internet booking for our wedding and wondered if we knew the person. It was his dad, who showed up 2 hours before we got married, half-lit, and refused to put nice clothes on. When he showed up, he said he wanted to surprise us. Who the hell surprises someone at their wedding?
I take my DH's lead in how he wants to handle these things. He is constantly let down by them, but is not ready to cut them off, so I smile pretty and keep my mouth shut. If it was up to me I'd tell them all to go to hell and stop hurting my husband. But, its his family, so I let him tell me how he wants to deal with it. Someday I hope he'll be ready to tell them all off, but that day is not today...