First didn't the deal that Picard helped set up for the people of Dorvan to stay there (under Cardassian rule) also cover other colonists in that region who wanted to stay?
No. The decision the colonists made was such an unexpected and unlikely one that Picard would hardly have even considered extending the offer to any other colony. Certainly no mention was made of any other colony choosing to become a Cardassian possession. Most probably opted for evacuation, or then stayed put but on the UFP side of the border.
To me that sounds like they gave up their rights as Federation citizens in order to not have to leave their homes.And that's why both the Federation and the Cardassians saw them as terrorists.
No dweller of Dorvan V was ever considered a terrorist by the Feds or the Cardassians, that we'd know of. The terrorists came from elsewhere; most came from planets belonging to the UFP but existing inside the DMZ where the UFP was forbidden from providing military aid to the UFP planets in question. Whether the DMZ even
existed at the time Picard made the deal with Dorvan V is unknown; possibly it was created as an "alternative way out" after the events. (The writers only invented it for DS9, but that doesn't mean it wouldn't have been invented earlier on in-universe!)
As explicated in the last Maquis episode, "Blaze of Glory", the Maquis never gave up their rights as Federation citizens. They
were planning on declaring independence (which would have had this legal-practical result), but they never worked up the courage to do that before the Dominion squashed them. So for their entire history, they remained UFP citizens guilty of crimes against the UFP. And of course against the Cardassian Union, which may be a crime under UFP law, too, even if Starfleet secretly wanted to give 'em medals for it!
If they were still citizens, wouldn't the Federation still be required to defend them if the Cardassians attacked them.
No doubt the treaty about the DMZ had clauses saying that if the Cardassians attacked first, the UFP could retaliate. But the Cardassians never did attack - they only did underhanded villainy where "rogue individuals" rather than the Union attacked the UFP settlers inside the DMZ. And there the DMZ treaty explicitly forbade the UFP from sending military aid.
It was only much later, when the Dominion entered the picture, that there was an open military attack against the Maquis (and the non-Maquis settlers sharing their planets with the Maquis). The DMZ ceased to exist then, legally and practically. But there was nothing Starfleet could do at that point, as the Dominion military was the superior one.
Ironically, there was an open military attack against the Maquis by
Starfleet, in "For the Uniform", made possible by the sudden weakening of the Cardassian Union. Whether the Cardassians filed a complaint is not told; they readily agreed to certain practical arrangements after the fact, though.
Timo Saloniemi