We are now engaged in a fierce war against a hidden enemy.
Doctors and Rabbis have both argued, and experience has shown us that the only way to overcome this enemy is to practice social distancing. 
This is especially difficult for us, observant Jews, as our pride and our strength lies in our togetherness and our unity. 
But there is no greater mitzvah than "and you should guard your souls."
Therefore, the mitzvah of the hour is to prove our love for one another precisely by canceling minyanim, be they in a parking lot, street, courtyard, balcony, roof, or any other location.
There should be no minayn held anywhere or in any way
While we will be physically separated, we will all stand with one heart and one mind in order to keep the mitzvah of saving lives, both our own lives, and the lives of those around us. So too, on the night of the Seder and throughout the holiday, we will have no guests and we will not visit anyone.
Only the immediate members of our households will have Seder together. 
Rabbi Shlomo Riskin - Mara D'atra