Thank you for your query.
I think you have had a twin conception, out of which one is non viable.
The spotting / brownish clotting is because of the non viability of the second one ( the failed second pregnancy
As a yolk sac
and embryo is visualized in the other sac, and if a heartbeat is clearly seen, it means that particular fetus is growing normally.
As the pregnancy appears to be dichorionic diamniotic ( two separate sacs as you mentioned ), chances of the non viable twin affecting the other are less, although not absent.
Continue taking adequate pregnancy support as prescribed by your gynecologist for the viable fetus.