Being young and famous has its perks -- because duh -- but there are also some occasional downsides that come with being a constant member of the spotlight. And that goes double for a pair of siblings who share the attention the way Kendall and Kylie Jenner do right now.

Currently, the Jenner (along with, of course, their Kardashian half-) sisters are pretty much at the epicenter of all pop culture-ish attention, whether intentionally so or not. But they aren't the first sisterly duo who've had some fun in the sun.

Hilary and Haylie Duff, who grew up on our TV screens by way of "Lizzie McGuire" and "7th Heaven" respectively, also have major life experience keeping it in the family. And the Duff sisters told ET Online that if they had to give the Jenner ladies a piece of advice, it'd be to stick together -- no matter what.

"Be each other's number one support system and always be on each other's team," said Haylie.

Imaginably, the heat gets cranked way up on sibling rivalries when we're throwing Ferraris and major modeling contracts into the mix, but according to Hilary, sis should still be number one for LIFE.

"It makes life a little challenging when everyone watches everything you do. To have a support system from your sister, and your sister be your number one fan and advocate is really important," she said.