As Roger explains you cannot transmit from one radio (= one chip) simultaneously. I guess you are asking if nRF5x can advertise on all 3 Adv. channels (37, 38, 39) during one adv. interval and the answer is YES. This is how Nordic stack (Soft Device) work by default in GAP Peripheral/Broadcaster modes, it emits 3 Adv. packets in short time (remember that it must to listen for short time window after every adv. Tx) so it appears that there are 3 "almost" simultaneous packets sent. But you can restrict adv. only to two or one from three adv. channels. If you are not using Nordic stack then you need to ask stack provider or write this yourself.
