The DSL speed will depend on the service type and also distance to "the telephone box" or central office.
Mine is about 1200kbps download and about 150kbps upload.
If you have 24 computers on one DSL line, you are not much better off than 56kbps on a good day. If you are all on line at the same time, forget it.
Yeah, A router would help, but 24 people? Only option is, get another telephone line with DSL installed. That would help a bit, but double your cost. More accounts or IP addresses probably would not help, just another type of line or more hard lines.