I hate hate hate cockcroaches so I can very much empathise with you! This sounds pretty serious, especially if they've spread... I would call in professional help at this point (eg rentokill) and (1) ask them to get rid of the immediate problem - most important!, (2) ask them to identify how/why they came from so you can learn if applicable, (3) ask for preventative advice for moving forward and maybe if there is a troublesome area that needs attention (a grate etc). There is no real cost for peace if mind here. Really good luck on eradicating these creepy crawlies!
Lil Bookworm