I once heard a very funny radio interview with a guy, who was once asked by his wife which of the children he loved the most. He said he loved them both equally, but then admitted he'd lied, and that he loved his sin much more. Obviously, there is some artistic license in there, but you get my drift.
There are always tensions and rivalries in families, some more acute and toxic than others, and nothing in the world throws a spotlight on to them like a wedding. Now is the time to understand those issues and make sure they don’t play out in your speech.
For me, siblings don’t play a major part in a father of the bride speech themselves, but you need to be aware of the context of what you’re saying about the daughter who is getting married. For instance, don’t be tempted to declare that the day she was born was the greatest day of your life…or suggest that you have never been as proud as the day she graduated. I have lost count of the number of times that I’ve seen howlers like this is in a father of the bride speech, and those comments will come back to haunt you at your leisure.
Whatever you say on the day will stay with you for the long haul, and the fact that you made contentious comments in a public setting, makes them all the more powerful. They may be unwitting in your opinion, and just your attempt to add emphasis to what you’re saying, but there will always be those who won’t see it that way. As always with wedding speeches – err on the side of caution.