the easy answer is to change Michael Douglas's character's name to Vernon Van Dyne, and Paul Rudd's to Hank Pym. Problem solved.
Hank is blonde. I don't want to see Paul Rudd bleached but I agree with you about Michael Douglass' role changing.
And with the storyline I suggested, Hank Pym is a scientist who's desperate to become a hero, so he creates a few robotic monstrosities to terrorize a major city just so he can save it. Things kind of go haywire and he can't shut them down which causes a number of innocent people to get hurt.
Moreover, his wife and the daughter of his mentor catches him in the act while he's having a nervous breakdown in which he completely snaps at her. I'm not sure if he has to go full Alabama Man on her but something to show that Hank really, really steps out of line.
It's the guilt that drives him over the edge along with his wife not only filing for divorce but threatening to stop Hank's machines by herself. Hank is forced to make amends for everything he's done to drive his life to ruin, starting with finding ways to destroy his own creations.
After he manages to save the day, he also reconciles with Janet, saving his marriage as well. Upon turning himself in, he finds that he gets a mysterious pardon from a government official who demands that he instead do community service in a way that's completely, "off the record" complete with a new alias called, "Yellowjacket" since the world knows Hank Pym/Ant-Man as a convicted felon who's allegedly serving time in a federal prison. The catch is that his community service sentence is thirty years of work for a group known as The Avengers.
That is how you do Ant-Man. You don't do two stories at once. You don't find a way to keep Pym off the Avengers. You don't have the woman who's usually Pym's wife be his daughter which is actually really messed up. You make a movie about redemption about somebody who starts out as being the most unlikable jerk in the world with a crazy ego problem and have him eventually become a real hero.
One consistent theme needs to be Hank's struggle with bipolar disorder. He's a hero with a disability and one that's more often associated with villains. A big part of his arc is recognizing that he has a problem and working to conquer it. Moreover, it's realizing that even though he's emotionally unstable and prone to violence, him being a jerk and his ego problems are his own fault.
The sequel would have Scott Lang be the villain who's an ex-con with a sick daughter doing jobs for the Kingpin and wants to steal Pym's original Ant-Man armor to help with heists. Pym eventually lets him have it so his daughter can live since he may disagree with a life of crime but he's not willing to allow a kid to die. After the credits, Cassie Lang is shown alive and well and Hank has sponsored her for the Avengers Academy.
