For the purposes of Banner of Command, Baron Buff, and Elixir of Ruin,
What else can be affected by them that aren't lane minions?
Do they all stack?
For the purposes of Banner of Command, Baron Buff, and Elixir of Ruin,
What else can be affected by them that aren't lane minions?
Do they all stack?
"Lane minions" is a redundant term, because all minions move down a lane, and there are no "non-lane minions". Therefore, whenever an effect refers to minions, it means nothing else but the melee, caster, and siege minions that spawn every 30 seconds.
Baron buff, Banner of Command, and Elixier of Ruin do stack their effects on minions. You can have a banner-promoted minion that is affected by all 3 minion buff auras.
Referring to your second question, this question (second answer) adressed the bonuses of Banner of Command and Baron buff added to each other.
user 5061 also explains how he calculated the numbers.