Are these malefic positons for the planets? What are the effects of Ketu in 2nd house and Rahu in 8th house, especially during the mahadasha of Ketu/Rahu?

It is better to have a specific horoscope in mind as the results can vary based on other planetary positions and which signs Rahu and Ketu are sitting in. But in general, this a person with this combination can have danger from food poisoning, snakes, drugs/medications, harsh speech, problems to spouse, and possibility of unexpected gains (i.e. gambling). Please remember this depends on many factors and this is just a generality I have seen in many horoscopes.

-WebYogi-

It depends on the lord of those houses.

Ompuneet-