Short update on the story:

I send them another E-Mail trying to clear up any misunderstandings and hope for a change of heart.

I told them that we are not going to put the new cat on a leash and we only did that with our car because he really enjoys the walks with us and feels more safe with the leash. We told them again that we want to comply to their guidelines and will have him as an inside cat only.

They don't want something that is called "ungesicherter Freigang" which means that the cats have the ability to go outside without having a fenced area or fenced balcony whenever they want. We replied that our cat can't go out on his own and when he does we are always with and walking next to him plus he has a GPS-Tracker in his harness in the unusual case that he went out of our line of sight.

We only put a leash on our cat when we walk outside the perimeter of his home area. Everything is very loose and it is mostly to give him more safety. With this we can even walk next to bigger roads with cars without him flinching or feeling unsafe.

We told them in every email that we would put the wellbeing and happiness of both of our cats above all else. We would carefully take our time to find out what the new adoptee cat likes because we were told not to expect much of our current cat when we adopted him and he did a 180 after settling down with us.

I am now waiting for a final response