2.6 seems a little early. I believe in early intervention, but sometimes it's tough to differentiate between delayed development and a disorder in toddlers. However, it's good that you've already begun OT/ST
Choice of language depends on the environment. If most people around speak Tamil then go for that. ST should be more in regional language and English so that he faces fewer difficulties in school. I can't tell the frequency without seeing him. Twice/week sounds good to me though. 5/week can be done too if it's not too strenuous for the child.
2-3 is the age of parallel play (and not cooperative play) and we don't see a lot of socialization in school at this level. If the teacher is ok with his mingling, then don't worry.
I do not want to be hasty, but I am getting a sense of a child who may benefit from SIT (auditory-motor, specifically) and PECS for developing instructions following/responding skills.
Thanks for the response and suggestions. From last 3 months he is undergoing ST and OT in local therapy center here and frequency is 6 days a week.
He can read the alphabets and numbers on the board and now therapist working to identify the objects using flash cards