The yellowing pattern of your citrus leaves resembles that of a magnesium deficiency, not iron.  Symptoms of iron deficiency are quite different as you can see here: go to http://www.ipm.ucdavis.edu/PMG/C107/m107bpleaftwigdis.html#CLOSE and then scroll down about half way to images of both iron and magnesium deficiencies,.) I suggest you don’t remove any live woody parts until the plant recovers.

 

You didn’t supply any details other than those about adding an iron supplement. Understand that even when the deficiency is corrected, some leaves won’t re-green.  Assuming that this potted citrus received regular doses of citrus fertilizer according to label directions, it should not have any deficiency. I suggest you re-pot the trees in fresh potting mix to avoid whatever is currently occurring in the rootball, and then proceed according to the information here: https://www.garden.org/ediblelandscaping/?page=201106-how-to. Also see this from a professional grower: https://www.fourwindsgrowers.com/tips-and-advice/growing-dwarf-citrus/in-containers.html