Kriyas Shema 4:2

One who married a woman who had already been married before was always obligated to recite Shema. Even though he was also occupied with a mitzvah, it is not as preoccupying. The same is true in similar situations.

Kriyas Shema 4:3

One who loses a relative for whom he is obligated to mourn is exempt from reciting Shema until the deceased is buried because his mind is distracted. One who is watching a body is also exempt from Shema even if it’s not the body of a relative. If two people are watching, one should watch while the other goes to say Shema, then they should switch. The one digging the grave is also exempt from Shema.