Is sikdar caste brahman

yes mostly, but not all.

Sikdars are either Bengali brahmins (erstwhile surname Bhattacharya), who were given the title of Sikdar by britishers. Sikdar means owner of one siki of land (which is 1/4th). They were the zamindars in Bangladesh's Sylhet region.

One of the msot famous brahmin sikdar is Radhanath Sikdar, GREAT MATHEMATICIAN AND DISCOVERER OF MOUNT EVEREST

There was hoewver, OBC sikdar also, who migrated ages ago from kashmir.