Albert Barnes Commentary Exodus 24:9

"Then went up Moses, and Aaron, Nadab, and Abihu, and seventy of the elders of Israel." — Exodus 24:9 (ASV)

It would appear that Moses, Aaron with his two sons, and seventy of the elders (Exodus 19:7) went a short distance up the mountain to eat the meal of the covenant , which must have consisted of the flesh of the peace offerings (Exodus 24:5). Joshua accompanied Moses as his servant (Exodus 24:13).