I'm almost glad you're going "batty" TBH !!

I just mentioned the other day how much I missed you around here.
I have a couple ideas for you:
Call the local DEC office (Dept. of Environmental Conservation) - they might be willing to relocate the little fellow, or recommend someone who could.
Next choice would be your local Cooperative Extension service office extension.org will help you find your nearest office if you're not sure. I happen to work at one of these places and we get calls all the time for everything from bedbugs to bees to bears (doesn't have to be a "B" word, but it's interesting we're talking bats). It's quite possible they might have a connection for humanely removing and relocating him.
Otherwise I'd suggest looking up wildlife rehabilitators who might be willing to help or have another contact.
If there is a rabies outbreak however, you might not be able to get someone to move him (there could be an ordinance to destroy bats). So if you know where he/she is getting in, you could possibly patch the opening (at night so he's not trapped inside), then he'll simply
have to move.
We had bats in our home growing up - in the attic and sometimes they'd fly down the chimney and out of the fireplace into the living room!!

Let me tell you, that is one big surprise! My parents had to patch up little openings in their attic/roof and they've been bat-free for a long time.
Hope everything else is going well for you, and that your sister is doing well!