The new royal baby is now 5thin line to the English throne and will move up places in line of succession, on deaths or abdication of any or all of the following:
Therefore theoretically, the new baby could become king. However it is very unlikely as a third child to become king. The last third child to be King was William IV who ruled 1830-1837. Conversely, could the fact, that the new babies, siblings, share their names with William IVs parents be a sign of the new babies destiny? William IV parents were George III and Queen Charlotte.
With everybody, living longer then it is unlikely everyone listed above would die before Prince George and Princess Charlotte have children. If and when Prince George or Princess charlotte has children their children push the new baby, down the order of succession.
Given there are rules about too many heirs to the throne travelling together; it is unlikely that all the heirs would die at the same time. Unless god forbid, someone plants a bomb in Windsor Castle 19thMay when it is the wedding of Prince Harry and Meghan Markle and that kills all of above. But the new baby does not go to the wedding being too young. All very far fetched as the security at the wedding will be intense and the baby will probably be in attendance.