Lowering number of bridemaids

Myself and my fiance are getting married next year and have already had to postpone my wedding 3 times due to covid. I was suppose to be having my 2 neices, my cousin my partners sister and his 2 brothers wives as bridemaids i want to cut down my bridemaids to just my 2 neices my cousin and my partners sister as i have relised i am not that close with his 2 brothers wives but my partners mum have already bought their dresses how do i tell his mum and also them i no longer want them as bridemaids and do you think i am wrong for feeling like this