We had a very similar setup... we lived next door to my MIL who has a HUGE double-lot which she keeps a little bit overgrown. They LOVED it out there during the day, and at night, they came upstairs with us and lived in one of those BIG airline dog crates. One of them also LOVED to play with our cat! Clyde would peck at the cat's collar tags and the cat kept trying to step "over" her to make her his "girlfriend".
He never succeeded.... but it was HYSTERICAL to watch.... they just ended up going around in circles.
The one that still lives with my MIL is in LOVE with my FIL. She follows him everywhere, "bowing" to his shoes, making that "eh-eh-eh" ducky-love noise!
That's AWESOME that your BFs DS takes such good care of them... animals do amazing things for people, dont they? Id LOVE to see a pic of their costumes!!