Is it obligatory to make up and offer expiation for one who gets water into his mouth and nose during ghusl to avoid scrupulousness, despite his certainty that the water has reached his interior even after trying to expel it, and does this affect his fasting?

He who doubts the emission of semen is not required to perform ghusl, because the default assumption is that it has not been emitted. The person afflicted with whispers (waswasah) must completely disregard them and pay no attention to them; this is the only cure for them. So, if he doubts the emission of semen, the default is that it has not been emitted, and ghusl is not obligatory for him. If he does perform ghusl, he should not overuse water. There is no need to worry about something entering the stomach; if he becomes certain that water entered his stomach unintentionally during rinsing, there is nothing upon him. As Sheikh Ibn 'Uthaymeen, may Allah have mercy on him, said, the fast is valid if the fasting person does something that breaks the fast unintentionally.