Major wedding woes.... Need advice pls

So my fiancée and I have been engaged 2 months and very excited. My future SIL boyfriend wants to pop the question to her via flash mob. He's been married 2 times already and she's just gotten her divorce finalized in June. This would be mine and my fiancées first and hopefully only wedding. Anyway I kinda want to say something to his sisters BF. I feel like they are stealing my spotlight. Is that wrong?   ?