No. Flanking had that reminder text because, up until then, it was not possible for a card to get Flanking twice. Flankign is a triggered ability, and as such, each instance of flanking triggers separately. Same goes for lifelink. If a card has lifelink more than once, yes, it WILL trigger more than once. So go ahead, equipe Knight of Meadowgrain and smash in for a 15-point swing, they'll lose 5 and you'll gain 10.