To me, the family tickling thing is all about perspective. Long before I realized this was a fetish, at about ages 12 and 13, I tickled my two aunts feet, and they tickled me. At that time, I wasnt into tickling as a fetish, so it wasnt all an OMG how bad thing. It just happened. There wasnt anything sexual, or incestious about it, because, at that time, tickling didnt mean that much to me.
That being said, and considering my current perspective on tickling, I would now only tickle female friends, girls with whom there is a mutual attraction for, and a signifcant other/wife, when I get one. What one's perspective is at one time in life, may well not be what the perspective is years later. So, while aunt foot tickling didnt freak me out at 12 or 13, currently, it would be inappropriate, I wouldnt do it, and it would be weird.
Mitch