I agree with the above comments. He has his own room so why would a teenage boy want to share a bed?
Pay attention to how his father speaks to him and pay attention to how you do it. If you think you’d need to adjust how you speak to him, do it. My nephew only listens to his mother instead his father because his mom says it sweetly like, “honey, can you please go take the garbage out?” Vs his dad yelling, “Hey! Take the garbage out!” He won’t listen to his dad. But with your son, it could just be that your son’s dad has more authority in his voice. Also, you SHOULD give explanation to why you need something done like hey, “I need you to sleep in the bed because xyz”. I don’t understand why you wanted him to do that though, as a teen, I’d ask why also. Teens value their own space a lot so I get his frustration was made worse when you didn’t want to answer his question. You should just have told him why instead of seeing the question as a threat to you because he’s “questioning your authority”.
He’s entitled to want and have his own personal space. Especially for sleeping, it doesn’t make sense to me why you would try and make a 12 year old share a bed with you and 2 small children? It’s not comfortable so I understand his reaction. My 12 year old is the same with his dad and myself, kids will play up with whoever they’re most comfortable around and usually that’s the mother. Dads tend to be more stricter so they will listen. That paired with hormones and puberty, it’s a tough time all round unfortunately!