There is an issue of Jewish law that one has to be aware of.
Unlike the Sabbath, on Yom Tov one is permitted to cook food, under certain conditions,
which I will not describe here.
However, one is not really allowed to cook on Yom Tov, for the benefit of
a non-religious Jew nor for the benefit of a non-Jew. [The Rabbis have derived this from their analysis of the Biblical text].
Therefore halacha discourages one in normal situations from inviting those individuals
as guests specifically on Yom Tov, (when Yom Tov doesn't fall on the Sabbath) because it might lead you to cook on their behalf. However, some Rabbis have found ways to solve the problem.
For example, my rabbi allows me to invite non-religious guests for Yom Tov, if I resolve to do all the cooking ahead of time and none on Yom Tov. In order to draw the non-religious Jews to Judaism, he would even encourage me in many (but not all) situations to make use of this leniency.
Other rabbis offer additional solutions.
Just bringing this issue up, if for some reason you have a strong reason for wanting to invite non-orthodox or non-Jews. This year the first day of Passover falls on Sabbath.
Another issue to be raised with a Rabbi, is that some Gentiles for one reason or another become so impressed with the idea of the Seder, that they themselves start practicing some warped form of a Seder, each year. Even President Obama is doing this, at least while he's in the White House.
You have to ask a Rabbi if encouraging such type of behavior is a good thing or a bad thing.
Conclusion: If I haven't made myself clear the question of who to invite to the Seder is too delicate, to give a straight yes or no answer in an internet forum.