You can ask him anything but what I am wondering is.... Why it matters when the sister's boyfriend asks her? The focus is still going to be on the wedding plans at hand cuz yours comes first. Or am I misunderstanding the question?
Is it inappropriate for me to ask my fiancé to ask his sister's boyfriend not to propose 1-2 weeks before our wedding? Because that is what he plans to do.
No, it's not JUST inappropriate . . . It sounds like it may also be selfish as well . . .
Be happy you have the spot light you have . . And if need be, share a little of that light.
Yes .. It's highly innappropriate for you to interfere with someone else's plans for something that doesn't concern you .. Why would you begrudge such an event? Because you don't want them to steal your 'thunder'? .. 2 WEEKS before your event? That just sounds obtusely selfish as it has no bearing on your event. Your wedding and the time leading up to it will not be shaddowed .. It will be inhanced .. Or at least it should be. If it were my family or friends .. I would be ecstatic for them.
When someone gets engaged, it is supposed to be a happy time .. And you of all people should appreciate the meaning of such an event considering it happened to you. Be gracious and let them have their moment .. and be happy for them taking such a big step .. no matter how close to your event it is. This event does not reflect on you or your wedding .. it has little to do with your plans .. period.
Although it is unconventional to share with others the 'date' or plan to propose marriage .. In this case, it sounds as if this plan was perhaps told to someone in confidence...and THAT should have not been shared with anyone else. That's definitely a shame. Not a lot of people adverstise openly that they intend to take such a step.
It is an understandable preference, but it is inappropriate---for any of the good reasons mentioned above.
But why would you want your sister to unknowingly postpone 2 weeks of her happiness for you?
Believe it or not, but it's really not all about you. Learn to share, that's my advice. It makes life a lot simpler and easier on everyone.