Complex sentence: Donny formerly sang with his brothers Alan, Wayne, Merrill and Jay as The Osmonds; younger brother'Little' Jimmy Osmond later joined the group as well as having solo success.
Split into simpler sentences: Donny formerly sang with his brothers, Alan, Wayne, Merrill, and Jay, as The Osmonds. Their younger brother,'Little' Jimmy Osmond, later joined the group as well as having solo success.