Grammatically, you’ve split the first part of your sentence “After discovering they’re adopted…” from the rest of the sentence. So replace that period with a comma, first up.

You’ve described TWO protagonists, when it helps to identify who the central protagonist is – whose journey we’re going to follow. Even Thelma and Louise or The Shawshank Redemption have protagonists.

Taking a road trip to find a compatible bone marrow donor is not a logical action to take after finding out you’re adopted; my guess is that, while finding out they’re adopted might occur in the first act, this is not actually the event that kicks off this story.

So – refocus the POV to a central flawed protagonist, adjust what the event is that kicks off the story:

‘When only a bone marrow transplant will keep her alive, a defensive adoptee crosses the country with her burnout sister to find the only compatible donor: her biological mother.”

I’d suggest trying to find the source of antagonism; who exactly is making this road-trip difficult for the characters?
Likewise, it’d be very easy to include a time-clock to up the tension.

It sounds like one of the problems everyone is having over and over with this concept, and with each version of the logline, is that they’re unable to see a clear trajectory that the story is going to follow. The potential for conflict is there, but what form the meat and potatoes of the script will take is not concretely defined. As a result, it’s hard to gauge the tone and genre of the work. (Does he move his mistress into the home under the pretence of her being a live in maid? OR does his wife agree to the new living arrangement, and if so, what is the thread that begins to unravel? Does he leave them both? Does he confess to his wife and she leaves him, so he tries to make it work with his mistress and discovers he doesn’t love her …)

Which is why I think everyone is pointing out the need for a clearly defined GOAL. Once he learns that his mistress is pregnant, and he wants to raise the baby AND maintain both relationships (both very human, very relatable desires), what does he actually DO that forms the backbone of your narrative?
– It’s kind of like that film Locke … if Tom Hardy had gone home in the first act and immediately fessed up to his wife and tried to move his mistress in. The concept sounds like this definitely has potential, but it’s unclear how it all works. This logline doesn’t sell it well enough to want to know more.

My first suggestion would be to simplify the language you’re using in the logline, and to avoid being vague about anything (I’d drop the reference to “fame as currency” and “paying a hefty price.”)

“After a celebrity impersonator learns that both his wife and mistress are pregnant, …”

What happens next?