Ask an Alim

Source 1 : Sistàni, Minhàj as-Sàlihine, vol2, p76, m232
مسألة 232: لا ربا بين الوالد و ولده و لا بين الرجل و زوجته فيجوز لكل منهما أخذ الزيادة من الآخر
Proposed translation : [The law on the taking of ] interest does not apply between a father and his child, nor between a man and his wife. It is thus authorized for each to take interest from one another.

Source 2 : Sistàni, Minhàj as-Sàlihine, vol2, p76, m233
مسألة 233: لا فرق في الولد بين الذكر و الأنثى و الخنثى و لا بين الصغير و الكبير و لا بين الصلبيو ولد الولد، كما لا فرق في الزوجة بين الدائمة و المتمتع بها، و ليست الأم كالأب فلا يصح الربا بينها و بين الولد
Proposed translation : Whether the child is a boy, a girl or a hermaphrodite, it does not make any difference. The same applies if he/she is the older or the younger child or the grandchild.

There is not any difference between a permanent or a temporary wife. On the other hand, the mother does not have the same status as the father; the taking of interest between her and her child is none [forbidden].

Answer to question 1 : The taking of interest between a father and a son is authorized. It is the same for a father and his daughter.
Answer to question 2:
a.    The taking of interest between a grandfather and his grandchild (granddaughter and grandson) is authorized.
b.    The taking of interests between a husband and his wives (permanent and/or temporary) is authorized.
c.    The taking of interest between a mother and her child (son/daughter) is invalid [and not permissible].