Hi
You should proceed with a partition .
This can be done either all of you together reach to a settlement to divide it in equal portions.i.e of each of you 1/7parts.
Six children and mother all have equal rights including married sisters.
If one of the brothers who objects doesn't agree for an amicable settlement your option is to send another for partition through lawyer and procedures to file a partition suit in the civil court .
Your brother has no special right ,has equal right with you ,siblings nd mother .
If married sisters are opting out if share due to their shares are settled at the time of marriage in terms of shtridhàn ,can give NOC to their shares