S.H.
1) My son LOVED his crib, slept GREAT in his crib, and was in his crib until 3 years old. Then one day he asked to be in a regular bed, so we did. And he had no problems being in a bed or sleeping in it.
- an option would be to put a mattress on the FLOOR, for your eldest child to sleep on.
2) Per potty training. The child needs to be ready. And even if the child does potty train, "night time dryness" is something that does not occur until even 7 years old. Because it is according to their organ development and physiological development. Not per age. So you will still need to buy diapers, for night time.
3) And your child seems to be, not ready for that.
If you start pushing toilet training now, there will probably be a LOT of battles and frustrations about it. For both your child, and you.
And he is not talking much etc. so I would think, you need to wait.