I'm not going to let my daughters go to their half-brother's wedding because it's too far away
That sounds sad. Why would you stop them from going to the wedding?
I just think about the costs and whether the trip is really necessary.
You don't have the right to stop your daughters from attending their half brother's wedding. Where there's a will, there's a way.
I'm going to cancel their flights and stop them from going. I want my kids to spend more time with me, not their annoying half-brother and his family.
You can spend time together after, they want to be there on his big day, and you should respect it. You might not get along with him but your kids will resent you if you deny them this once in a lifetime chance.