Julz a second opinion is not a bad thing, but I get that you are irritated since it's you - and it's usually us moms - who is always doing the doc shlep and probably loads of reading and research otherwise, only to finally have your decision questioned. As if you don't know when there is something wrong with your child, are making a decision for surgery lightly, and are just going along with what the doc is telling you.
I think you're on the right track allowing Neil to take Dylan for the second opinion so that he can hear directly from the doc about what's going on. And it's a good thing that he is concerned enough about his son to do this.
In the end you both love your LB and want the best for him and the two of you working this out together - even if you're coming at it from opposite sides - should lead to a good solution for Dylan. I know that I'm not always happy having my decisions and choices for my LB questioned by his father (or anyone else for that matter!), but if I think about it, there is often something else to consider. And even if I end up sticking to my decision, this questioning and consideration of the opposite side will reinforce that choice (ie I was right all along and now I'm even more right

)