Expectant parents Kym Johnson Herjavec and Robert Herjavec are over the moon that they will soon be welcoming twins. “This has been a roller coaster for them the last few years – meeting, falling in love, getting married and now starting a family,” a source tells PEOPLE about the couple’s nearly three-year romance. (The Shark Tank star is already a dad to three children from his previous marriage.) “Kym has wanted to be a mom for a long time. They’re both so happy,” says the source of Johnson