Hi MistyMom!!
I also have 2 kitties (Bling and Minky) but they are already 6 years old. We had a 'stray' come and decide he wants to live here in June. At first I did everything to get him out but he kept coming back (cat flap) and I would spray water at him, shout, my cats attacked him. He just never left.
I then started feeling guilty that this poor kitty has no home and it's winter and here I am throwing water at him. so I let him in....and kept him...
I named him Zakumi and put up posters in the complex with photos to see if anyone claimed him. After 3 days no one did and he was beginning to spray in the house so I decided he is now mine and I'll neuter him, vaccinate him etc etc.
so I did!!!! That was the Thursday....he stayed all day and night, ate the expensive food, slept on the bed. My cats hated him so much but he just saw their attacking as playing as he is still young.
On the Sunday I was on a course and DH was at home. He called to say the owner came and took Zak back!!!!!! I was heart broken

I went to her unit to demand him back (she didnt miss him for a full week so why is she coming now....) and she wasn't home. but I heard Zak inside crying and crying so then I was also crying and trying to get him to jump onto the window ledge so I could steal him back!!!!!
Anyway, the next day I spoke to the owner. She looks very simple and didnt even know what I meant when I said he's been neutered. She didnt even know what the vaccination card was....I offered to buy the cat from her and she said no, it's her baby blah blah blah.
I was not happy...but decided maybe it's for the best since we are immigrating and taking 2 cats is expensive enough.
Well, a month later, he is back. So since July, Zak spends every single day here. He comes around 4-5am and leaves around 6pm. He eats a HUGE amount of food, sleeps on the bed with my 2 cats, plays with them, lies on the couch. And I've decided to just leave it.
She cant love him that much if she doesnt even wonder where he is during the day. They dont have a cat flap and live on the upper level so surely she knows when he goes out at 4am he cant get back in until the evening......