People from families where passages from the Haggadah are skipped during the Seder need to know what is absolutely required. I've never seen it spelled out explicitly except in regard to soldiers. Here is the relevant parts from what R. Nachum Rabinovitch advised soldiers who are in an emergency situation (Melumedei Milchamah, no. 83):
On the Seder night there are two biblical commandments and four rabbinic:
A. Telling the exodus story --
1. When you can take a Haggadah with you, take it and say as much as you can.
2. In an emergency situation, say: We were slaves... and God took us out; Our ancestors were originally idolators; Pesach, matzah and maror based on what...; the blessing on the Ge'ulah...
D. Hallel -- There is no need to say it at the place of the meal, and you should say it wherever you are...