As has been mentioned, they WILL come out eventually. I suggest you sit quietly at least 4 feet from the couch. Don't bend down to look under to see what they're doing. Talk in a soothing voice, if at all. No TV, no Stereo. No standing up or moving around, stay seated on the floor.
Have a toy with you that makes interesting sounds. Crinkle ball on a string, wand toy with tinsle, etc. Move the toy around on the floor so they can see it, but again don't look under the couch, just let them observe the toy. If you see them coming out or peeking, don't look directly at them, avoid eye contact until they come out on their own, just keep enticing them with the toy.
It might also help if you have some nice smelling cat treat on a plate for them.
Maybe some fresh boiled chicken morsel or similar.
Once they come out, make no move to touch them, let them explore around, they will come to you very soon. ( I know it's not soon enough, but they'll get around to it!)
Bengal kittens are motivated by toys and food, you should be able to win them over with this routine.
Good luck and have fun!