According to scholarly commentary from the NAB:
Psalm 72 is a prayer for the secular king, "[a] royal psalm in which the Israelite king, as the representative of God, is the instrument of divine justice and blessing for the whole world. The king is human, giving only what he has received from God. Hence intercession must be made for him. The extravagent language is typical of oriental royal courts. The crown prince is the king's son; the prayer envisages the dynasty."
Re: from sea to sea, "The boundaries of the civilized world known at the time, from the mediterranean Sea (the western sea) to the Persian Gulf (the eastern sea), and from the Euphrates to the islands and lands of southwestern Europe, "the ends of the earth". The words may also have a mystic nuance, - the nuance surrounded by cosmic waters, hence everywhere."
Re Isaiah 33:24, variously refers to a) heaven, b) the current church on earth, c) Israel and Jerusalem after the overthrow of Assyria, and d) after the millenium when the New Jerusalem comes down, onto the new earth mentioned in the Book of Revelation, far in the future.
Nothing in these verses remotely suggest a two-tiered system as the JWs envision.
See these commentaries. http://bible.cc/isaiah/33-24.htm
For addition research sources, here is a long list:
http://www.144000.110mb.com/directory/jehovahs_witnesses_research_resources.html
If you are really serious about dispelling this two-tiered salvation plan of theirs, spend some time here; it ends the discussion:
http://144000.110mb.com/144000/index.html
Remember, the 144,000 is only one side of the coin. Disproving the great crowd on earth is the other.
Hope this helps.