Bridesmaids thank you card

Hey everyone ! I have three months left I’m trying to get everything together because thanksgiving and Christmas also new year’s eve is coming up so that will take up some of my time that’s why I’m trying to put all the last little touches for the wedding together now my question is and I knows it’s to soon to ask because I still have three months or less till the wedding for thank you notes for the bridal party do I have to write a long message ? , I have my sister as maid of honor my 14 year old niece as junior bridemaids my cousin my fiancé twin sister and also his sister in law also my sister best friend because she’s like a second sister to me since I’ve know her for 12 plus years I’m not having a hard time writing a thank you note to my sister or niece , cousin sister best friend the only ones I’m having a hard time really writing a long message to is my fiancé sister and sister in law can I just write thank you for being a part of our day and showing us support !? Or will that seem kinda coldhearted ?