I have 2 questions about the tag-along feature: 1) how do you get the character tagging along to disappear when you get him/her and 2) how do you get the tag-along character to stand side by side when you are talking, instead of the leader on top of the tagalong?

I can answer the first one:
Use the [*link-up] icon then follow that with either a full stop "." or a "-" minus.
So, [*link-up]. or [*link-up]-
Alternatively you can write [*link-up]=0 as suggested in the messenger.
If you need this to happen instantly, just have some text after you make the tag character appear, then on a page sometime later, make them disappear as above.

As for controlling the position of the tag-along, I'm not aware of any way to manipulate its position, or direction. They simply follow you.

If it just looks odd, perhaps on one sprite, activate the tag character to follow.
Then make the player step forward onto a new sprite, which activates the rest of your scene. Then you won't be standing "on top" of the tag-along.

Good idea. This may not be necessary for talking to ordinary sprites, but for those big important scenes, you could deactivate your tag along and then switch on a sprite.