That completely depends on the set of twins. One may find stories of twins being interested in the same person in the news, but twins often find different partners or may even have different sexualities.  Polyamory in twins is not unheard of, but it’s not because they are twins. Siblings, friends, or even people who share similar preferences or have the same sexual orientation may fall in love with the same person. But, one needs to follow polyamorous relationship rules to thrive in such a relationship.