Ohkayy I have a question everyone!

This is my second child , but my first pregnancy I wasn't so excited but I'm so glad I have my son , but anyway I showed my SO family the ultrasound n they said that baby was really big for 8weeks & twins run in their family n hide behind one another or something  n that they believe it's two babies because when I was only 4-6 weeks n took the test the line was really dark when they showed up ! Anyone that's having twins have very dark lines