Hello,
I owned a comet goldfish for 6yrs before my mother accidentally killed him.  I also have one who is 4yrs old and has grown tremendously he is very happy comet named Brutice.   I love the fish so much I decided to buy 2 new ones I have the right size tank, filter, live plants too.  They do not seem nearly as active as my four yr old.  All they have been doing is swimming on the bottom behind a plant together...is this normal?    

How big is "right size tank" for you? A 30 gallon is absolute minimum for three streamlined fish.

I'm already going to point out that you probably didn't put the new fish in quarantine before introducing them? This is very important, unless you completely trust that the shop you bought them from has only healthy fish. You still need to quarantine any newcomers for at least 2-3 weeks while treating for parasites, and observing water quality and the behavior of the fish.
These two fish might just be sick, especially if they're not particularly active.

So if I was you, I'd start with testing the water for pH, ammonia, nitrite and nitrate. If these are all fine, I'd suggest you looking closer at the new fish (and the old one!) so you'd see if there are any other visible symptoms on your fish.

It could be, if you put them there sometime yesterday or day before that, that they're simply not used to the new environment. It usually takes a couple of days for fish to acclimatize and get comfortable in their new home.

They are in separate tanks than my four year old,  both new comets are only 1/2 inch they did not have any larger ones at the store.  I have only had them for 3 days but I think the first response was probably it.  A lot more active today maybe just getting use to surroundings.  A 20 gallon tank for the two might seam large to them right now also.   PH is good, I am no sure of the plant though I grew them from a kit in the pet store with an few different types.  Thank you for your responses I appreciate the help.

Definitely agree with Nossie. The bigger the better, I definitely don't think it would scare them as it would feel more like freedom  And what fishie doesn't like a lot of space to swim around in? You will be suprised at how quickly they grow and I know Hanna can back this up as her two comets grew very quickly. Then once they grow they will produce more waste and not only will the tank be to small physically but chemically.
How big is the tank? And how are they doing? Hope all is well