My advice is, don't tell them. It sounds like they're not into tickling, and they may not understand this. And is it really that important for your family to know about your love of tickling? I would think you'd enjoy tickling a lot more w/a Sig-O as opposed to your sister, or your mom. Plus since you just met them last year, they probably have a lot of their own personal secrets that you don't know about, and it's not always appropriate to share that info.