How should I deal with the whispers of the devil with regard to ablution and purity?

Whispers in ablution are from the devil, and so you should take refuge in Allah from the devil`s evil suggestions that aim to distort the religion. Thus, once an organ is completely pure, don`t question its purity since having whispers doesn`t mean that the purity is invalid as it has already been established.

Is Fajr (dawn) Sunnah a confirmed one?

All praise be to Allah The Lord of The Worlds                                                                                                                                                                                  Of course, it is a confirmed Sunna which the Prophet (PBUH) used to offer in a regular basis. And Allah Knows Best.

Is it permissible to divide one mudd of fidyah between two people?

No, it is not permissible to divide one mudd between two people, because it would not count as a full meal for either of them.

Is it permissible to consume the meat of a sacrifice (Dhabihah) offered as an act of devotion to Allah, seeking His protection for my family?