I disagree the ER tech wouldn't say anything. They can list possibilities if you ask, but they aren't allowed to diagnose you. I had vanishing twin and two techs and the er doc on call made zero mention of the second sac until I asked. They did refer me to an additional scan to confirm what it was though.
My suggestion is get your ER file. You have a right to it. There may be a printing fee but usually you can get it as email. You'll see the doctor's notes and whether it was labeled yolk or a twin.
Me, personally, torn. The bottom one has got some clear budding and a head. The other I feel like I see something that looks like a head but it looks more snowman than gummy bear (if that makes sense). It honestly looks more baby than yolk to me but I'm not a gyn =\. Can you ask your regular gyn to take a look at the ER notes?