Is he allowed to choose between fasting for two consecutive months and feeding sixty poor people as expiation for having intercourse with his wife during the daytime in Ramadan after Fajr, and is expiation obligatory for his wife, knowing that she was pregnant?

If a traveler arrives during the day while not fasting and has intercourse, he is not obligated to abstain from food and drink for the rest of the day, nor is expiation due from him. However, if he arrives before dawn and has intercourse while fasting, he must repent, make up the fast, and offer expiation. The expiation for intercourse during Ramadan (definition) is: freeing a slave, and if he cannot find one, then fasting for two consecutive months, and if he is unable to do that, then feeding sixty poor people.

As for a pregnant wife who fasted and fears for herself, there is no expiation due from her for intercourse, because she is in the same category as a sick person for whom breaking the fast is permissible. If she fasted without fearing for herself, then she must make up the fast and offer expiation if she was consenting. If she was coerced, then she only needs to make up the fast.