Are Toga Siblings?

While that theory may or may not be true, its basicly confirmed toga has atleast one older brother and one younger sister. She was refered as 'eldest daughter'. Not 'Eldest child' or 'only child', or even 'only daughter', but 'eldest daughter'.

Are neito and Toga siblings?

Monoma Neito and Toga Himiko are Siblings - Works | Archive of Our Own.

Are Toga and Bakugou siblings?

I think a lot of people believe that Himiko Toga and Katsuki Bakugo are siblings, but they're not. Yeah they have the same hair color and look quite similar, but their biological information is basically the opposite.