Applewatchs8 is dual-card. Can both calls come in?

You can't. According to the user guide of Apple Watches 8, the dual-card of Apple Watches 8 can only receive telephone messages from data-enabled cards in cellular mode. Applewatchs8 dual card can only talk to one of the incoming calls when it receives two incoming calls at the same time, and the other incoming call can only start talking after the last incoming call is completed in the background, so applewatchs8 opens the dual card and the two incoming calls cannot come in at the same time.