That is amazing news! I am so happy for you! Get ready for double the work, double the love :)
Congrats on your twins :)
It is quite normal to bleed during pregnancy, especially with twins. Your embryos are embedding deeper, and your uterus is expanding at a rapid rate. Think about this-they want your lining at 8mm for transfer...that is about the size of a pencil eraser....
Drink 80oz's or more of water everyday. It helps to keep your uterus hydrated. And try to keep your feet up as much as possible.
I bled from week 6 to 16 of my twin pregnancy. Pretty much every. Single. Day. Red, brown, gushes, spotting, you name it. My twins are 3 1/2 yrs old.
Also. Do NOT panic if heartbeats are not seen tomorrow. It is sometimes closer to 7 weeks before they can be detected.