Hey, going thru this ATM with my two year old DD also !!!!.....we put DD #2 recently in with DD#1 as DD#3 moved outta our room.
DD#2 thought it was party time. SHe would run up and down the hallway after we had put her in bed !!!!. She was eventually falling asleep, but that wasnt till 830pm. SHe would sleep thru the night though(unlike your son....). But she would wake at 630am - very early for her.

Anyway to cut a long story short, she went from being the best sleeper in the house (whilst in her cot) to the night time terror (in her new single bed......). SHe ended up getting gastro, a cold, and was basically a nightmare during the day (so tired....). So last night we moved her back in her cot in her own room. Our DD#3 is back in our room. I hate it, and i had a little tear (my plan didnt work....), but she was suffering, and i really think at 26months, she is just too little yet to understand the consequences. She's too young to reason with also.

If i were you i would put him back in the cot, or even put him in a portacot, if it means you get rest, so be it. It seems the situation isnt working for anyone at the moment.....i dont know if ive been of much help. But good luck, i know how precious sleep is during 3rd tri.....