i'm struggling with this one. i have 2 cousins who are sisters, let's call them jenny and josie. josie's husband proposed to her before jenny's did. josie and her husband had already sent their wedding invitations when jenny and her husband got engaged. jenny and her husband set their wedding date for a time before josie's, even though they had been engaged first. everyone thought that jenny was TA for stealing josie's thunder. i can see how people would think that about you. however, there are more nuances to your case than my cousins'. either way, setting your wedding date before someone else's in the same family when getting engaged after them will put a bad taste in everyone's mouth, but since you talked to C about the wedding you wanted, it's a little bit suspicious of her to set her date so close to what you wanted. but then again, how was she supposed to know you'd be getting engaged so close to her?