My ggg-aunt who was the great-grandaughter of Ezekiel Rigg (son of Clement) left notes on this family.Here is what she has:
Clement Rigg, gentleman farmer married Rachel Owens near Norristown Montgomery Co. Penna - Issue 1. Clement m Miss Clarke lived at Brandywine Manor.He was a farmer. 2. Rachel died single 3. Keziah m Abraham Worley and lived on the Susquehanna. 4. Hosea was a Baptist Minister and lived near Mechanicsburg 5.Eleazer m and lived in Illinois (on the side a note says Mrs. Erskines father I suppose also Mrs. Battle & Mrs Bakes? perhaps their grandfather. 6. Ahijah m and lived at Redstone Washington Co. Penna 7. John m and also lived at Redstone Washington Co Penna 8. George married Mary Uptogrove and lived in Morgantown Penna 9. Ezekial m Margaret Moore.They had five children; Hannah, Hiram, Ezekiel, Peter & Margaret 10. Elisha an Episcopal M married Jane Atlee of Lancaster Penna sister of Dr. Atlee surgeon.They lived at Wye easternMaryland and he was buried in the church.His widow was 80 years old when I saw her at our house in Reading Penna about 1845.Issue - 3 children William, George Washington, & Atlee.William d single, George Washington married and had 3 children William, Eliza & Theophlus.Atlee died on the desert of Arabia
Abijah died single.
Since Robert is not listed he may have died young after his grandfather's will was written.