No. For faction guardians, both of them can have any rank, level or other status, it doesn't matter.

Ok. I was thinking about FW because in Barbarian i have: Lego: Scyl and epic: Fahrakin, High Katun, Aina, Alika, Armina and Sikara.

You're asking two separate questions.

To the first - champion level does not matter at all for the purposes of faction guardians.

To the second - no, you probably don't want two of them for faction wars. Though that said, Aina, Alika, and Sikara aren't terribly good either.

A very good champ for barbarians fw is the rare Soulbond Bowyer. She can reduce the tm of an enemy by 100%, very helpfull vs. the faction bosses, and her A1 is an AoE attack, perfect for a stun set. I completed the Barbarian faction with two rares in my team, Warmaiden and Soulbond. Don't look just at epic and legendary champs, some rares are usefull. Only a few, but it's worth to know wich rare can help.

From rares i have Warmaiden and Soulbond Bowyer. Will try them in FW. First i look in Ayumilove or Hellhaides for best Barbarians for FW

Also worth noting is that soulbound Bowyer is great for a dth secret room. I brought two to 60 just for that.

i built two soulbound's for DT secret rooms as well.  she's good for eternal dragon SR4 and frost spider SR5.  solid long term investment.

Sikara is the only other worth building.  her remove buff sped my team way up, but requires a tanky build.  Skip Aina and Alika unless you're down to fw21 and need someone for it, otherwise you'll probably pull someone better before then.