Hello all,
I am wondering if any of you could give me a hand?
ill start from the beginning,
back in October I acquired a coffee plant, about a foot high with another 4, 3 inch tall coffee plants growing around it.

the big 1 foot tall one and a couple of the 3 inch tall ones did quite well until November/ December, in which case the big one started wilting and produced a yellow leaf here and there, I thought "must be dry" so I watered it and it came back to life. wilted again about a week later and repeated the same thought, then It finally clicked that, OH all of these plants are trying to live in this pot it came with that is only 3 inches wide, perhaps its too small. So I upgraded it to about a 5 inchs ish (forgive me im not good at guessing measurements) clay pot, I thought ok all is well.

The plant acted quite a lot better after the move but after about 2 weeks the same process began again, so I thought "must be too many plants fighting for the same water", so I separated all of the plants into individual pots leaving the large coffee plant (which had a surprisingly small root ball, compared to how tall it is) in the big clay pot, they wilted a little but after the move and a good watering, the big one perked back up and I thought hallelujah its going to live, but to no avail it just keeps on wilting and occasional dropping a yellow dried up leaf leaf however the yellow leaves have decreased in occurrence. But it has one now as you can see in the attached picture.
I have had it in a couple varied sun light configurations and none seem to improve its situation, since getting it it was in a north facing window, and seemed to do alright however was in the direct fire of a furnace vent so the humidity was low, but still seemed to do well? since I live in the great white north (Canada), I thought that maybe it wasnt getting enough sun so I have tried it in direct sun that lasts about 4 hours or so a day (when not cloudy), and I think it wilted worse than it ever had been, as well it was getting a slight draft from another furnace vent and noticed the pot was actually getting warm from the vent, so I just moved it to a partial sunlight spot, and with no drafts, but again, no improvement.

I have looked on the internet but the people I find with a similar problem either find no answer or else they get told that a yellow leaf here and there is normal and that its wilting from transplanting, or else they get told to run water through the soil to help wash the salts out, which ive done with no improvement?

the soil I used was regular garden soil (as in soil from our local dirt) which does not drain the best, and does get hard packed after multiple waterings, but I have combated that by putting sticks in the bottom of the pot to aid in draining and ruffling the soil to help dry it out, as well as keep it from packing.

please feel free to ask me any other questions, and I hope someone can help me save the poor tree lol.

please forgive me if this is hard to understand, I am not totally sure where to start, and what all you guys might need to know.
Thanks for your time and help in this matter
Donnyh13