Ugh. You all must be exhausted. If he's happy and fit during the day, I doubt he's hungry at night. Sounds like separation anxiety.
I have 2 kids as well. My 9 mos old started doing that about 5 weeks ago. She was waking screaming for me (even if my husband went to get her which he would because he couldn't handle her crying) and insist on nursing to fall asleep. She didn't do this during the day. She did it because she wanted to be around me, so as soon as hubby left town for business last weekend, I started sleep training her. I used the Ferber* method and luckily it's been going well. She goes down at 7:20pm (the first night was at 8pm) and sleeps 12 1/2 hrs at night; I do hear her wake but she goes back down immediately on her own. On average, it takes most kids 3-4 days and at most, about a week. She does still cry for a minute like she's mad when I put her down and when I go in to get her in the morning. But she's been perfectly happy during the day and even better temperamentally too. Since they share a room, I let my clingy 3 yr old, who's a terrible sleeper, sleep in my room this week. I prepared him by telling him we would be teaching HIS little baby to sleep this week and that she would cry a lot. To minimize disturbance, I put on white noise and close the door to her room and to mine. When I sleep trained him, I had to just let him cry it out and he was perfectly happy in the morning and throughout the day too. And I tried everything with him. But I still have to sit with him for him to fall asleep. I will train him yet again Super Nanny** style next.
Some will say that to let your child cry is cruel. But your child can't talk yet, so there's no other way to express stress, tiredness, or any other displeasure. If you've had a full day of activity and stimulation, don't you just want to cry too? Also, to tend to every need of your child, he'll never learn to cope. There's a lot of mamas out there who will disagree with me, but no one ever let my older one cry or let me let him cry, and now he's super clingy and cries every time he is displeased.
No, I'm not heartless. I will say that this is the third time I've tried to sleep train her since August. Prior to that, she was an angelic sleeper, then she became a horrible sleeper. She really wasn't ready (nor was hubby). She screamed for hours then was super clingy the next day. So, it's been a good 5 months of no sleep for me.
*Ferber isn't letting them cry it out all alone. You put them down sleepy but awake. They do cry, but you do check in on them, without picking them up, at successively longer intervals. So, first you wait 1 minute, then you go in and tell them it's okay and you love them. Then you wait 3 min, then 5, then 7, then 10, then every 15 min. from then on.
**Super Nanny goes something like this... sit next to them but with your back to them, no communication. If your child gets out of bed and comes to you, you put them back in bed with no talking. Every few minutes, you move your stool a little further away until you are out the door. The next night you sit just a little further away and keep moving away. Eventually, you are out the door.
Every child is different. Every parent is different. Good luck to you finding what works for you.