Hey,
I am new to the site and I was looking for some ideas for bride and bridesmaids dresses. I want to stay with a Ren look mainly Celtic garb possibly mixing in tartans since the men will be wearing kilts, but I also don't want my friends to hate me. Ideas?
Well, if their your friends hopefully they'll love you no matter what you do

I suggest talking it over with them first to see how they feel about it. As for garb, are the groomsmen renting formal kilts or are their kilts more garb like? If its the latter you can always do a simple chemise/irish dress combo. Many grab sellers have this combination at a reasonable price and some like Very Merry Seamstress do them as bridal party packages.
If its the more formal kilts you might consider doing a simple, more traditional bridesmaid dress and then pair it with celtic knot jewelry or a shaw/drape/wrap with either tartan or celtic knot patterns.
For wedding dresses with celtic flare you might want to check out threads of time as well. Good luck and hope you have a wonderful wedding.