Brahman realization does not mean that "My brother is Brahman, and I am Brahman, and all others are not Brahman." This is not Brahman realization. Brahman realization means to introspect the spiritual existence of all living entities. That is Brahman realization. Samaḥ sarveṣu bhūteṣu. Then that oneness is still not sufficient. That means you have to engage yourself in Brahman activities. That is perfection. Therefore it is said that samaḥ sarveṣu bhūteṣu mad-bhaktiṁ labhate parām (BG 18.54). After this Brahman realization, actual devotional service begins. Brahman realization means that "I am spirit soul and the Lord is the Supreme Spirit." Nityo nityānāṁ cetanaś cetanānām (Kaṭha Upaniṣad 2.2.13).
He is the Supreme Spirit, chief living entity, and we are innumerable, without any number. Asaṅkhya. The living entities are innumerable. These are stated in Vedic literature. The very word is used, asaṅkhya. Asaṅkhya means without any numerical estimation. And God is one. God is one, but the living entities are many. Nityo nityānāṁ cetanaś cetanānām. So, eko bahūnāṁ yo vidadhāti kāmān. That one is the supreme one who is supplying all the necessities of living entities.