Okay, I'll take this a bit at a time, and that might help when others read and want to help:

"Travel expenses of sole owner of rental condo with SO accompanying her."

What are the specific travel expenses? Is this a mixed purpose trip?

"Her expenses only would be deductible on "maintenance" visit if he did not perform any maintenance duties, correct?"

She owns the property, and might need to travel to it to oversee maintenance and repairs. She doesn't even need to be the one doing that work. Him doing or not doing maintenance is a separate issue. And what is "maintenance" visit in quotes? Is that an artificial classification for the trip: "I know, we'll call it maintenance, but we'll just take our vacation there, since it's empty."

"On a non-maintenance visit neither would be deductible, correct?"

What I think you are trying to figure out is "business" trip? For instance, to the property to check up on the tenant, collect rent are not maintenance, but are part of being the landlord.

"In the first scenario"

Which is a maintenance trip or a "maintenance" trip? Or, is the first trip description the part of her only vs her and him?

"would splitting the vehicle expense"

Mileage, or actuals? Is there enough distance that lodging and meals are involved on this trip?

"while at the location be entirely or half deductible if vehicle for other than passenger transport?"

What did they ride in, if that wasn't a passenger vehicle? Did they take a bus? Rent an RV?

More specifics and details always help.

Have you read the IRS resources:

https://www.irs.gov/businesses/small-businesses-self-employed/tips-on-rental-real-estate-income-dedu...

https://www.nolo.com/legal-encyclopedia/deducting-landlord-out-town-travel-expenses.html