Feralasys1 (I like the name, btw), I believe the Ranked Team borders will only appear when playing with the same Ranked Team. If you duo with your cousin outside of your Team, it may not appear. Is that possibly what happened?
Kigiras, were they in the same queue? The 3v3's have a different Elo Tier threshold than 5v5's, and Teams have a different thresholds than Solo. For example, 1200 might be Silver on 3v3's but only Bronze on 5v5's. Is this possibly the case?