That's a cool approach that you've suggested--"being a sounding board and source of encouragement". I don't necessarily need to say "I think this". Instead, I can encourage him to tell me what he thinks and encourage him to have talks with his kids about what he thinks.

I do believe that the ultimate decisions are to be made by the dad, the mom, and the kid. I hope that any time I do express an opinion, they understand I'm saying, "Here's a piece of information, but absolutely y'all decide what you're going to do, and I'll support you."

I believe in unified command--if the kids see the parents (or dad's girlfriend) disagree, they can get confused. I like when parents decide amongst themselves what they're going to do, and then I honor that and verbally support what the parents decided should the kids ever ask me.

Any time kids asked me about a sensitive topic, I'd say things like, "I think that's one of those things that are good to talk to your mom and dad about."