Putting toddler to bed on their own?

hi my son is 3 im march, he still falls sleep on the sofa and i carry him up once he is sleep, if i put him to bed to fall to sleep on his own then i would have him up for hours screaming the place down. im also on my own with 3 other children and preg with my 4th. so i just think, i have other kids who need to sleep to and its not fair that they hear my toddler screaming for hours so for all our peace of minds and less stress i put him to bed when he has fell to sleep. and if that's what works for us then that's what i will do. i have the choice of 20 mins falling sleep on the sofa or 3 hours of screaming. its what you feel works best for you. i done the same with my other son and when he was 3 and started nursery it all stopped he went into his own room in his own bed, i think they change a bit when they start nursery/school