PS.... you're in a sticky situation, eh? I think a lot of people have given you good advice, and you have a good head on ur shoulders, and should be able to work things out. I do agree that it is your wedding, and you should be able to have it the way you desire. I also know for a fact, that when you marry a person, you marry the whole family. And so, his parents' wishes and opinions do and will matter, now and in the future. Just wait, the fun has yet to begin.
But this thread is about your wedding. My only suggestion, have your parents talk to his parents. Your parents have the authority to put their foot down and have their wishes for their daughter respected by his parents, and still respect their wishes too. If you say you want the mehndi, yes, you appear selfish. If your parents say "we want this for our daughter, we did it for our other daughter, it is our family tradition, and we want to give our daughter away with the same love and happiness" it will come across better. Talk to your mother. Have her talk to your future MIL. Work this out through your parents, and I think you should be able to take the "brat" smear off you.
You could always let them know that Mehndi isn't a Hindu rasm at all. There was no henna in India before the Muslims came...the Turks and Persians brought it and all the customs associated with it from the Middle East. And the way Muslims celebrate Mehndi ceremonies in Pakistan & India today is virtually identical to the way its still celebrated in Turkey.
You are vey well read Masha Allah! quite a valid argument.
Ive told them there will be a mehndi because its a family tradition but it will be a small one.
Thank you all for the input and ideas! I appreciate it! :)
If i may say: there is no point in having a smaller function instead of what u wanted initially .
The inlaws view is that mehndi is a hindu tradition/ waste of money, it still is even when you have a smaller one.
What im saying is, your stilling having your mehndi. I dont think this will be seen as a compromise.
You could rather have what u planned initially.