Electing people from the same family does not make the country a monarchy.
On the contrary, electing sons, wives, brothers ad. perpetua is just as bad as electing FDR to four terms, and requires the same solution, a constitutional amendment.
You mean like Bobby and Ted Kennedy?
Looking at that analogy, the Kennedys, this is not unknown. RFK very probably would have been elected in 1968, had he not been assassinated. In a 20 year period, the Kennedy family produced 3 candidates for the presidency.
While I do not expect Jeb to run in 2008, it is possible that there could be 3 Bushes in 20 years.