Ipad2 and iPhone 5s using iOS 8.3 and iPhone5s would like to update

I have an ipad2 with version 8.3, which I plan on keeping so I don't lose the ability to play my older games. I also have an iPhone 5s with the same version(8.3)

. My question is, if I update my iPhone 5s to the latest iOS 9.3.1 (keeping ipad2 on 8.3) will they still be compatible with other? Meaning will I receive my messages, photos, contacts, etc on both.