Do you salute a senior officer when walking alongside an even more senior officer?

I concur..

I have saluted cars w placards knowing there is no way in the world they could see me. When in doubt.....

Some time ago, I saluted the then Vice-President. Are we supposed to salute the Veep?

SP5 Joel O'Brien - .....
Always Salute A Superior Officer.
And That Includes Most Of The Park's Squirrels,

"When in doubt, whip it out." How about this though: each group is led by a LTC, each has a CPT, a 2LT, and an SFC... Pass each other with a cancelation non-salute assumption, or all salute by 2s with the two SFCs left in a held - salute until the rest are done or gone?

Again everybody. If a higher rank officer approaches you salute. When an approaching service member salutes you it is returned by you so everybody salutes.

Nothing complicated about the example you chose:
The SPC, 2LT and CPT _all_ simultaneously salute the LTC.

The LTC returns their salutes.
The CPT with the LTC exchanges salutes with the other CPT at the same time that the LTC is returning the salutes
The SFC salutes the CPT and 2LT at the same time that the LTC is returning the salutes.

I Believe The ONE SOLUTE Per Day Rule, Only Applies To Warrant Officers...
~~~ I THINK. ~~ And For Me, Thinking Is A Rarity,

Informal formation - gaggle.

LTC Yinon Weiss & MAJ Bryan Zeski - Gentlemen; I suspect that you are both correct(ish).

The way that I'd call it is "If you are WITH another person then the senior of the group is the only one who counts and the GROUPS salute as per the relationships between the senior members and it is the senior members who salute for the GROUPS. However if you are only with another person then you are a group of individuals and have to follow the code as individuals."

Face it, if you are a group led by a Lieutenant that is marching past the Camp Commandant and the Camp Sergeant Major then it is only the person in charge who salutes and it is only the Camp Commandant who returns the salute. (It would be highly improper for the Lieutenant to salute the Camp Sergeant Major and s/he would have to complete their salute to the Camp Commandant BEFORE they could return the salute of the Camp Sergeant Major [who would have to wait for the Camp Commandant to return the Lieutenant's salute before s/he saluted the Lieutenant as it would be highly improper for them to return a salute directed at the Camp Commandant].)

If you had two groups with Group 1 composed of an E-1, E-3, E-5, E-7, E-9, P-2, O-4, and an 0-6 and Group 2 composed of an E-2, E-4, E-6, E-8, O-1, O-3, O-5, and an O-7 and if each pair of salutes took 30 seconds to complete, you would spend almost an hour (56 minutes to be exact) just getting the "meeting" portions of the salutes done AND, since you would (obviously) have had to stand still to get those salutes done then you would have to spend the same length of time to get the "departing" portions of the salutes done.

If each pair of salutes took 30 sec of complete, you might have quite a few that qualify for the Special Olympics.

... which begs the question: "What if they have no arms... Are they still required to salute?" And if they are junior and don't initiate the salute, do you, as an officer, still salute them?