Using a checkbox group for selecting multiple people would make for a simpler interface, but I suspect it wouldn't be flexible enough for you and it would require a lot of space on your screen.
You might consider using a two field approach with a script. Selecting a name or names in a drop down with a script trigger to perform a script that adds the selected ID to a second field--the one actually used for your portal--either as a filter or a key in the relationship. You can add a clear button that clears this field. It may even be possible to set up your value list to dwindle. (Selecting a person removes them from the list so that you can't select them a second time until you clear the field.)
"Is there a better solution to relating this one-to-many (Properties with many People) relationship?"
Yes. use a join table between properties and people. That way you have one record in the join table for each person connected to the property.
PropertyID_pk > PropertyID_fk (Join Table) PeopleID_fk < PeopleID_pk
This way you eliminate the VL problems in Problems 1 & 2.
I think Bumper has the better suggestion here.
Well, I'm funny! I had originally looked at the Invoicing template that came with FM, but thought that to be overkill!
What I didn't consider at the front end was how important the Property to People link would become in my application.
Bumper and PhilModJunk, I really appreciate both suggestions and will apply both to my database, because I now see a different place to use PhilModJunk's suggestion. It'll be perfect.