In Q1 you cannot omit the second
that (
that land) because it is the demonstrative adjective, not the relative pronoun. The other
that can be omitted.
In Q2 the second and third
that can be omitted. The basic rule is that
that can be omitted as long as the meaning is not confused by doing so. There are other restrictions--
that cannot be omitted when it is the subject of the clause:
The dog that ate my sandwich has disappeared.
PS: Oh, I see-- you highlighted the wrong
that in Q1. Yes, the
that before
he could can be omitted, but the sentence is clearer if it is retained.