Complex sentence: After mulling it all over, they decide that having a child is not practical given Mark's life expectancy but Ruth still wants to be a parent, so in 1997 she and Mark apply to be foster parents.
Split into simpler sentences: After mulling it all over, they decide that having a child is not practical given Mark's short life-expectancy. But Ruth still wants to be a parent, so in 1997 she and Mark apply to be foster parents.