While all three are jealous, it would be a mistake to reduce any of them to that alone. For a moment, let’s complicate the characters of Regan and Goneril. As the eldest, Goneril might, by the rule of primogeniture, have expected to become queen of a kingdom Lear arbitrarily divides up; also, she has been married to a husband she despises, so that she might have good reason to feel hostility towards her father. Regan is differentiated from her by having a husband who matches her in toughness, so that she is driven to assert her authority, as being of the royal line, by upstaging him. Both daughters, like their father, enjoy the exercise of power, Goneril in bullying Albany, Regan in maintaining an edge over her husband by interrupting Cornwall when he tries to take charge (as at 2.2.132 and 146-148). If Lear had given both in marriage to much older husbands (Cornwall offers to be a “dear father” to Edmund (3.5.25)), their interest in the young and energetic Edmund becomes more explicable. It is ironic that not their ambition but their love for a man, Edmund, a love denied their father, makes them overreach themselves. Certainly, all of this does not erase their jealousy, but it does give the characters more complexity, which some of the details of the play support.
Yes, absolutely. It isn't jealousy alone in the case of any of the three, but it is definitely jealousy. In Edmund's case, it is jealousy of the socially approved status his brother has. In Goneril and Regan's case, it is jealousy combined with greed and a lust for power, and jealousy in a fairly straightforward fashion as far as their competitive relationship for Edmund.