Need some guidance

I’m fairly new to audacity and am trying to remove loud noises ( banging construction sounds and airplane) as well as some background noises ( hiss and hum of electronics ) while trying to preserve and increase the volume and clarity of muted conversations ( recorded from another room ).

Which types of effect should I try to tackle first and in what order ?

I don’t think using Noise Reduction is possible, as I am unable to isolate any portion of the track with just the background noises.

Low level noise can be reduced with the Noise Reduction effect, but you need to have a region of the recording that has only the low level noise.
It is not generally possible to remove loud sounds to reveal quiet sounds that are masked by the loud sounds.
If this question is regarding a covert recording, please note that recording people without their knowledge is illegal in many countries, and you would be best to seek professional advice in such cases.

Thanks, I have no concerns regarding the legality of my recording.

There is a phenomenon called “Rorschach Audio”, (like the ink blots), where noise is misinterpreted as words.
Digitally-processing the Audio, (e.g. applying noise-reduction), increases the odds of that happening, e.g.

Processing the audio rarely makes voices pop-out into being comprehensible, and can add artifacts which sound like voices.