Are blue dwarfs bigger than red dwarfs in theory?

Blue dwarf stars are hypothetical and the Universe is not old enough for them to exist if they exist at all. The theory is that due to the convective nature of red dwarf stars which makes all the hydrogen in the star available for fusion, the star would not expand as a larger star would expand to a red giant, hence their surface temperatures would increase and they would become bluer instead ( note blue being relative ). Therefore if such a stage exists then they would be the same size as the red dwarf star they once were as the premise is that they won't expand.

Yes. Significantly so. Think of blue dwarfs as being the red giants of red dwarfs. Though they're still small enough to qualify as dwarfs, mind you.

When the universe is old enough for blue dwarfs to exist, in about +200 billion years, they'll be about 1.5-2 times the size of the original red dwarf.

Hypothetically. The universe isn't old enough for any blue dwarfs to actually exist yet.