Hello to all!

I am extremely new to gardening, but last year possessed me to start trying, and i decided i wanted to use the avocado pits we got from store bought avocados. So i have two avocado plants, the tallest of which was the second one that was planted and it seemed to develop faster than the first one. But alas a year later I feel the bigger one has died (i enclose pictures for confirmation). I moved them indoors as i read that avocado plants do not like to be kept in the cold or in windy areas, and i think thats what set off what is seen in pictures. Now the second one has had my full attention but it too is, i think, starting to die.

I had them in jars and tall (old) cordial containers to allow a good root and small stem to shoot before i planted them in soil (i think it is ordinary soil that my dad had bought) and they were floushing in the summer. I never watered them too much as well (perhaps twice a week maximum) and they seemed to love it. Since they were moved in for the winter, i watered them maybe once or twice fortnightly (this was after i had noticed the leaves turning brown and falling off). I have not noticed any bugs whilst they were indoors, but only some small black spots under the leaves when they were outside (which i removed as soon as i found them).

Is there any comeback from the pictures, or is this post too late?
Thanks in advance for any help!!!

The plant on the left has always been the shorter of the two even though it was planted first and the plant on the right is the one that i think has died (although i hope it hasn't as it is still green on the bottom and has remained this way for the past month and a half).