If you are asking for a minor key that has only B-flat in it, then the answer is d-minor, but if you are asking for any minor key with B-blat in it, then you have; d-minor, g-minor, c-minor, f-minor, b-flat-minor, and e-flat minor (there is also a-flat minor if you are looking for an enharmonic key signature with 7 flats...).
A flat minor is the relative minor of B major
There are no flats in b-minor. B major has two flats, both B-flat and A-flat, but b-flat minor is the relative minor of D-major, which has a sharp key signature. The sharps in b-minor are F-sharp and C-sharp.
It's not a major, it's a minor. The relative minor of B major is G# minor.
F major and its relative harmonic minor, D minor, have only b flat.
B flat Major has 2 flats and G Minor has 2 flats.
A flat minor is the relative minor of B major
There are two flats, B flat and E flat. It is the relative minor for B flat Major.
Relative major and minor share the same key signature but a different tonic note (a tonic note is the first note of the scale or in solfege tonic is DO). For example, D flat major has five flats in it's key signature and b flat minor has 5 flats in it's key signature; therefore, D flat major and b flat minor are relative.
F# minor is relative to A major, so Gb minor is essentially the same, although they're probably looking for B double flat major or something useless like that.
There are no flats in b-minor. B major has two flats, both B-flat and A-flat, but b-flat minor is the relative minor of D-major, which has a sharp key signature. The sharps in b-minor are F-sharp and C-sharp.
It's not a major, it's a minor. The relative minor of B major is G# minor.
If I understand your question correctly: G minor has two flats, as does B flat major.
The relative major key of B minor is D major.
The relative major key to B minor is D major.
The relative minor of D major is B minor.
F Major has a relative minor key of D Minor and has the key if B Flat.
F major and its relative harmonic minor, D minor, have only b flat.