When I first saw current T, I told him I didn't want him to criticise T1. So he didn't.
Then about a year later I was criticising T1 and he was still trying to stay neutral, so I ended up getting angry with him. I later realised I hadn't told him that I don't need him to avoid criticising T1 anymore.
Since that mini-rupture happened, he has been more open with me about his negative feelings towards T1 including saying his behaviour sounded like grooming, and that I was "very wise" to discontinue communication with him. He has refrained from saying anything explicitly derogatory or from his own feelings, and I think that's because he doesn't see any benefit for me in that. I do have a sense of his feelings towards T1 now though. Sometimes it is as subtle as raised eyebrows when I recount something T1 said or did.