Still in the end if the martians had been able to control the orbitals around earth invading really would not be necessary. They could demand unconditional surrender or just start dropping rocks till the earth quit. The whole invasion of earth was not a question of taking out the whole thing it was basically planning for drop insertions to capture some specific points.
If GoT hits around April, which every season did except 7, it should wrap about the same time The Expanse airs assuming they keep the same release schedule they have for seasons 1-3. S1 Dec '15 > S2 Feb '17 > S3 April '18 > S4 June '19?