The feeding and cleaning regime sounds fine

. I would advise treating the main tank though with an anti internal bacterial medication as a precaution though as dropsy can be internal bacterial in nature (fortunately though dropsy is generally not very infectious)- it can be caused by many other things though (like tumors/cancer in the fish, water quality problems, unwanted chemicals in the tank water, NTD and Fish TB etc).
As to eunhanising fish, for a small fish like a guppy personally what i do is get a small bowl of water and put it in the freezer long enough for it to develop ice completely covering the surface of the water- i then take the bowl out, break the ice on the surface, and immediately put the guppy in the bowl. The temperature shock to the guppy will kill it in less than 10 seconds- i've used this method many times on guppys many times and it is guaranteed to kill the guppy quickly and with no mess.
There are a lot of other humane methods of euthanasia, like the clove oil or decapitation methods, and there are many threads on this sort of stuff if you want to check out further options- the temperature shock method is just one method i personally use on small fish like guppys.
ps: (for those others who might be reading this thread though, the temperature shock method is only advised for small fish like guppys, platys, neon tetras etc- nothing exceeding 2inches in length).