If I can get outside tomorrow, I think I'll be able to tell how those two are doing.

Literal

Tomorrow outside [to-に] go-out-can [if-ようなら], two-people [subject-が] how doing [subject-か] know [quotative-と] think [feminine-わ].

外にでられるようなら uses a complex conditional: potential form + ようなら ('if it seems possible'). 二人がどうしているか is an embedded question — 'how the two are doing.' The sentence-final わ is a feminine softening particle, marking the speaker as female.