"to give to them": those who entered the land. "and to their seed": their children. "after them": the lands conquered by David and Yeravam, viz. (II Kings 14:25) "He (Yeravam the son of Yehoash) restored the boundary of Israel from the approach of Chamath to the sea of the Aravah."
Variantly: "to give to them": those who entered the land. "and to their seed": those who came up from Bavel. "after them": those (who will come) in the days of the Messiah.
(Devarim 1:9) "And I said to you at that time, to say": Moses said to them: It is not of myself that I say this, but at the behest of the Omnipotent. "I shall not be able alone to bear you": Is it possible that Moses was not able to judge Israel? The man who took them out of Egypt and split the sea for them and brought down the manna for them and flew in the quail for them and performed miracles and wonders for them — he should not be able to judge them! — This is what he said to them (Ibid. 10) "The L-rd your G-d has 'elevated' you over your judges," (removing the onus from you and placing it on your judges!)