I didn't even need to read your whole post before posting whats wrong.

Those goldfish are likely to be Common goldfish, they actually require
20 gallons each - yep thats right. The reason they are lethargic is because
their waste is poisoning them. You need a filter for one thing - a filter
will eventually house good bio bugs which convert their ammonia into nitrites
and then nitrites into nitrates. Nitrites and ammonia (and high levels of
nitrates)
will kill your fish.

Your goldfish have the potential to grow to 12 inchs and live for 20 years.
In your 2.5 gallon bowfront they will be dead within 6 months, hate to be so
blunt but I'm just telling it like it is.

Find someone with a pond if you aren't willing to get a big tank, and definitely
do not consider flushing them as that is very cruel and a long linger death for
them.