Ghost catfish are very weird and sensitive fish. They usually take about a week or two to fully acclimate. Just give them some time. Also, they tend to not be the healthiest fish from the chain pet stores. You might have gotten some ones that might not make it.
But, after awhile, they will get more active and comfortable. I would suggest getting a hide/cave of some sort or maybe more plants. A little more coverage would help them adjust. And when they finally do adjust, I haven't really seen them school too much. They aren't like tetras. They will sort of group, but if you had a larger number, they would school more similar to characins. At your number, they probably won't stay together too much.
55gPLANTED:Rainbows/Loaches/Garras|30gVIV:Crestie|20gL:Leos|10g:Pearl Fighter|5g:Betta|5gChi:Spark Gourami/Badis|5g:ADF|2.5g:Betta|2.5g:Betta|