Tell them you are working with the other recruiters so if they don't want to double-submit (which invalidates the candidate in most cases unless the resume is so good the company does not mind paying double commission) they will have to tell you which companies they are submitting to. If they still refuse to tell - they don't work with anybody and just submit you to any open job ad they can find, you can do the same yourself with a lower chance of screwing up (e.g. the aforementioned double submission or the company explicitly rejecting any representation).