163,200,000lbs or 74,026,275kg plus 5% per year for everyone.
Or 1 general sherman just for the elves.
Assuming you have a way to contain the gasses. It takes six molecules of CO2 to produce one molecule of glucose by photosynthesis, and six molecules of oxygen are released as a by-product. A glucose molecule contains six carbon atoms, so that’s a net gain of one molecule of oxygen for every atom of carbon added to the tree.
A mature sycamore tree weigh 4000lbs, including the roots and leaves. If it grows by five per cent each year. The actual calculation is a huge mess, big trees grow faster than small ones, see source below) so we are ballparking it. It then produces about 100kg of wood, of which 38kg will be carbon. Allowing for the relative molecular weights of oxygen and carbon, this equates to 100kg of oxygen per 4000lb tree per year.
A human breathes about 9.5 tonnes of air in a year, (lets say elves are the same) but oxygen only makes up about 23 per cent of that air, by mass, and we only extract a little over a third of the oxygen from each breath. That works out to a total of about 740kg of oxygen per year. That is about eight 4000lb trees worth or 32,000lbs per person.
So for a rough ball park estimate your tree should be at least 3200000lbs or 1,451,496kg or roughly 1 General Sherman just for the elves. But it also means the tree needs to grow by about around 5% or 160,000kgs per year. So start with 3200000lbs and then add about 5% per year it has been supporting those elves.
keep in mind if those humans are using fire for anything, cooking, heat, ect. they need a LOT more trees.
Now lets add in the extra people this is easy, 32000lbs times 5100, or 163200000lbs and again add 5% for every year it has been keeping them alive.
Note:I did get many of the starting number from a BBC publication I use in class about this. xerox of an article. But I don't know the original author is, if anyone does, please post in comments and I will add it.
Just for the elves you need this.