No need to worry, as he is standing with support which is normal for his age . And for sitting place him on a hard surface 2 to 3hrs daily as it is difficult for him if he is on a foam bed or cushion and make him to sit with ur support.
Next Steps
observe for other developmental milestones like monosyallables(ma, ba) and try to give him a pen if he grabs and hold with 2 or 3 fingers its ok
Health Tips
donot always carry him , let him learn things