Does grouping up raise mmr?

So me (gold V) and my two friends (silver 1 and unranked) played flex and got grouped with a gold 4 and Silver 5 player (none of us were ranked last season). We faced a Gold V, Gold IV, Gold lll, Plat V, and Plat IV. So I just really don't understand how match making works in flex, does your mmr sky rocket if you're grouped or what? This isn't the first time the teams get stacked on the enemies favor either so I'm confused because when we all play solo/duo (individually) we face people on our own rank.