Marriott Residence Inns accept any number of pets! Hooray! So the plan is that we will spend our last night in Philly at the Marriott Residence Inn near the airport, with the cats. We'll request a late check-out and hang out there until it's time for our flight. When we get to Portland we'll do the same, but at the Residence Inn near the river in the southwest part of downtown (assuming we can't get a key for our new apartment until July 1st.)
Problem solved!
Thanks to all who offered advice.
Oh, and for your viewing pleasure, my latest Farm Town creation...