8 week old won't sleep in crib for long periods of time?

Hello, my 8 week old son will not sleep in his crib for long periods of time, he enjoys sleeping in his swing instead, I know it isn't good for his back to let him sleep in there. He will only sleep on his stomach also ( when my mother in law watches him, she does that!), I have been breaking that habit because i'm afraid of sids. Lately I have been waiting for him to fall in a deep sleep while he is in his swing and then put him in his crib, but then 5 minutes later he is crying, Is there anyway to keep him asleep in his crib? Do crib soothers help? Maybe a sleep positioner? Thank you for any help :)