Yes, not only were the sons of Elrond twins, it ran in their family, Elurid and Elurin were twins they were the brother of Elrond mother. Also Feanor had a set of twins Amras and Amrod.
As for Elven pregnancy, the closest I remember the books coming to this subject was that Idril got pregnant and gave birth the following year to Earendil. So it would seem their gestation period is the same but the age of maturity some have said to be at 50 years of age.