Baby developmental delay

Opinion needed from multiple doctors

Baby boy, about 10 month age,
Was born under weight, birth weight was 2400 grams.
Was born c-section.
Mother have three kids before this baby.
This baby boy is still very below on the developmental graph.
He has his own curve for weight, height and length which is below the standard.
He does not sit and crawl yet.
Doctor did MRI and it shows some damage to the brain at birth and as per Doctor it may be due to lack of oxygen to brain.
He does not make babling;
Now he started to make some notices , oun, aan ...
Doctor says he have global developmental delay, and he have mussel tone, legs and arms are stiff and shoulder and trunk is very floppy and due to that he can't sit till now,
Doctor says he have motor delays and specially he have more nod left arm and leg,
He kinda keep his left arm a bit twisted,
His neck and head is not completely controlled,
He keep head up for a little and the drop down,
He is going for Physio therapy and a little improvement is there,
He recognize mom, dad;
He like his siblings company;
He does eye contact and smiles as wee;
No issue with pee and poo so far,
Some time for a day he may get constipation;