Then (waw) here means “After that.” They shall take some of the blood means the blood of the slaughtered animal. And put it does not specify how the blood was to be applied. Probably Revised English Bible is correct in translating “smear.” New American Bible has “apply.” On the two doorposts refers to the upright posts on either side of the door opening that supported the lintel, the horizontal piece at the top. Good News Translation has “put it on the door posts and above the doors of the houses”; Contemporary English Version has “must be put on the two doorposts and above the door.” In cultures where houses do not have constructed framework for the entrance, one may say “take some of the blood and smear it on the sides of the entrance to the house and above the entrance.” The blood was to be smeared only on the houses in which they eat them, that is, “the houses in which the animals are to be eaten” (Good News Translation).

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .