I am sure you are right that the original establishment of only one captain, one lieutenant and one ensign per British infantry company was increased at some time during the Napoleonic wars. I think cavalry troops also had three officers originally (ie six per squadron) and again this was possibly increased later.
The actual establishments are in the Public Record Office at Kew. I looked it up on the internet and they have 1,178 establishments on file dating from 1661 to 1996. These do not seem to be available electronically so I will have to visit in the New Year. I would like to compile a list of all changes during the Napoleonic wars.
The only point I was making is that the ranks in any company were captain lieutenant or ensign. The senior officer, who should have been a captain, but on occasion was a lieutenant, was always on the front left of the company. The third most senior officer was on the left, whenever the company was in column or operating separated from the battalion. The second most senior officer and any additional officers were in the serrefile as a covering rank behing the rest of the company. Terms such as second lieutenant are appointments not ranks and an individual officer could change from second to first lieutenant and back again without any promotion or demotion, depending on casualties or new postings to the company. The term first or second lieutenant was merely a reflection of the seniority of the individual officers and not a rank as such.
Of course in action sometimes sergeants ended up commanding companies when all of the officers were casualties.