What were the first names of the Bobbsey Twins?

Nan and Bert were the older set. Flossie and Freddie were their younger sibling twins (4 years younger).

The Bobbsey family consists of:
The father, Richard, a successful lumber merchant; The mother, Mary (referred to at least once as "Edith"); Bert and Nan, slim, brown-eyed, straight-haired brunette, the older of two sets of fraternal twins; Flossie and Freddie, chubby, blue-eyed, curly-haired blonds), the younger twins.

https://en.wikipedia.org/wiki/Bobbsey_twins