told John that they can only communicate alpha-timeline to alpha-timeline.
So we have B1, which is in contact with A2. (kids and trolls)
And now we have B2, which is in contact with some universe that isn't B2. (kids and UU/uu)
B1 has an alpha timeline. B2 also has an alpha timeline. They are separate timelines, because they are separate universal instances. If you want to say they're all the "same" alpha timeline, you may as well throw out the concept of "alpha timeline" altogether, because the alpha timelines of every universal instance are "intertwined through paradox space".
If you want to keep using these words and have them mean anything, you have to concede on this point.