Outside: illness/disease 疒 (ice 冫, building 广), below: third/C 丙 (one 一 outside, two λ strokes inside 内 makes 3)
A disease that makes every third person sick.

Shows: inside 内 with one 一 further person 人, who is inside. (cf. third 丙)
Two connected 一 persons are inside, thus both

One 一, inside 内 (originally altar with sth. placed on it)
One 一 outside, two λ strokes inside makes: no. 3.

Left: hill 阝, right: corner and Third 丙 (one 一 outside, two λ strokes inside 内 makes 3)
At the hill is a corner with three (persons) who are vulgar and mean.

Left: tree 木, right: number 3: 丙 (here: image of a handle)
A tree that is third class, is used for handles/shafts.

Left: fire 火, right: third 丙 (one 一 outside, two λ strokes inside 内 makes 3)
The fire ahould be threefold to be brilliant.