Missions have specific minion movement rules.
But for mission 1
2. Stay, unless a move actually brings them closer. Say the objective is diagonal to the minion with a Mech orthogonal. The minion would move closer. It would not try to move around if the Mech is between the Minion and the object.
To build on this answer and offer an example, if a Mech is standing orthogonal to the Bomb in the Red direction in Mission 1, with a Minion diagonal to the bomb, the minion would normally prefer to move into the space occupied by the Mech (since it would be in the blue/green direction from the Minion). The Mech blocks it, but if the other space the Minion can reach that's adjacent to the Bomb is open, the Minion will take that path instead of staying put.
If both of those squares are blocked by Mechs, however, the Minion will indeed stay put instead of trying to move around the Mechs to an open square on the other side.