Who cares if anybody finds it weird? You should find it weird that they're so interested, in the first place. You have a close relationship with your sister, and you should cherish that while you can. Time has a way of splitting siblings apart, as you're already seeing for yourself. Soon it'll go from seeing each other every few months, to a couple times a year, to once every other Christmas dinner, to "I wonder if they'll send a 'happy birthday' text this year"...