Hello!
I need some *more* etiquette help!

My FI and I are invited to his cousin's wedding this upcoming week. He is an usher in the wedding. I will be 34 weeks pregnant at the time of the events. Our wedding is 11/30/13. His cousin sent out a facebook timeline on Saturday, telling my FI where he needs to be and when. They invited me to the page even though I'm not in the wedding or have anything to do with it besides being his fiancé. They put on the timeline that between the ceremony and reception, they will be doing a party bus. (This is very very common in our area, in fact it's considered different to not do this.) They put on there that there will not be room on the bus for ALL significant others and spouses of his cousin's (he's the groom) family, but if you are in the bride's family and are a so or spouse, you can come on first. I'm not mad about this, but his other cousin's SOs and spouses are. I won't be "participating" in any of the activities of the bus obviously with being pregnant, so I don't really mind not being on there. What is the proper etiquette on including SOs and spouses in the in-between time if you are doing something like this?
I know it's not recommended for there to be a break, but they are Catholic ceremonies that can't begin later than 2pm, and will be done by 3:15 at the latest. Most receptions will start around 5 or 5:30. We will have the same timeline, but we do have activities and a cocktail hour/appetizers during the break while the WP does the bus and has more pictures done. We have paid an extra $400 to be able to include all WP spouses and SOs in the bus in our break time. I feel like it's correct to include them because if not, they will be by themselves. (Especially the SO's who don't all know others at the wedding.) Any thoughts? (Basically, what happens on the bus is the WP drives around to other locations and takes more pictures and usually there is alcohol on the bus so it's pretty much the start to the "party.")
ETA: Thank you to everyone for your responses! I greatly appreciate it and feel as if you helped save me from an etiquette no no! I will be talking to my FI tonight about changing our timeline for our event. Also, I wasn't meaning that it was a "Catholic thing" to have the break, I was meaning that in our diocese, we are not allowed to have a ceremony begin later than 2pm so I wasn't for sure how to make it all work! Thank you again!