Due to your unusual family name of Dungan, I thought I'd look at the Internet to see what I coulod find out about them. I didnot find the answers you were seeking. However, here is some info and my conclusions.
William Dungan was born circa 1796 and died during the 1840's in either Fayette or Union Co. Ind. On 12/2/1819 he married Elizabeth Dawson in Fayette Co. (Elizabeth was born 1801 in Va.). Per the Internet (and you) they had 6 children, with son Robert being the 5 th. child. On the 1850 census of Union Co. were: Elizabeth and sons Thomas (born 1820-21) and Robert (b. 12/15/1834). Since Robert was the 5 th. child, apparently the other 4 were probably girls, who were either married or dead. If you could find a list of Union Co. marriages in the 1840's, possibly you could find the girls names. I looked at marriage lists for Fayette Co., and none were listed. Good Luck. Bob Eddings - no relation.