Rembrandts and Van Dycks hung on the walls

In her longing to escape, her thoughts turned to the high connections she still possessed. By birth, Johanna belonged to one of the great families of Germany, the ducal house of Holstein-Gottorp, and she remained convinced that with her family rank, her cleverness, her charm and vivacity, she still might create a better place for herself in the world. She began spending time cultivating her relatives by writing frequent letters and by paying regular visits. She went often to Brunswick, the glittering court of her girlhood, where Rembrandts and Van Dycks hung on the walls.

The above passage is from a book about Catherine II, the Russian monarch. Johanna was her mother.

Could anyone please explain who the men were in short? Thanks!