Hey guyz what can I do ?

hey guyz I m 18 n I ve a sis who is 24 older one and then my second sis who is 22 and them comes Me,,,Guyz I always wanted to kiss my oldest sis but I was afraid and my bonding with my second is too good we both are too close but I like my oldest sis the most...Me and my second sis usually kiss each other on lips and one day I told my sis that I want to kiss my oldest sis can u ask her if she allows me and then after 2 days my sis told me that we will go out together my oldest sis me and my second sis we all went out and she told me to stop in a calm place where no one is around we ll chat lis to music etc I said ok and then I stopped my car in a place where no one was around and my oldest sis told my second sis that go out and have a walk the time she went out my oldest sis told me that u wanted to kiss me then y did not u ask me directly...even I wanted to kiss you but just as a younger bro no sexual feelings etc I said ok n then she gave me a peck on lips etc but now her birthday is after 3 days n I want to give her a dress but i dnt knw her size should I ask her ???? that whats her figure size what can I doo ???