Here is an account of the migrations of the Gharri (Garre) people:
According to the Gharriβs oral traditional history and British colonial era records based on interview they had with then Gharri elders, regarding the origin of the Gharri people, the Gharri people came from red sea coast and settled at βSerarβ, what is now known as arusi province of Ethiopia, They build mosques and homes made of stones. Then during the 1600th exodus of peopleβs movement, from the north reached the Gharri kingdom and fighting ensued because the enemies started looting the Gharri properties and herds. The Gharri were outnumbered and they were forced to immigrate toward southwest, and settled around filtu and Wachile areas.
The Gharri traditional historians state that the Gharri lived there for period of about 60 years without any disturbances. During that time they build stone houses and mosques around filtu and wachile especially around the dawa riverbanks in around fifty miles corridors from Malka Mari through Malka Dirir area.as it were a standard way of building houses. Then later on the exodous of the Borana reached there. It was believed that was the first time they came in contact with the Borana
So, during late 1600 and early 1700, they lived with the Borana. Later on, things changed, and the Gharri were outnumbered by the Boran and the Borana tried to make them subjects and demand tribute. So, the Gharri decided to move back to their previous region of Confur through Juba land.
The "exodus from the north" is Darod Somalis from the Sultanate of Adal out of Ethiopia, specifically Ifat, which had been invaded by Amhara and Oromos, which forced Garre (of whom your ancestors were in the Garre confederation at the time) to leave their lands in Serar (Seraro in Oromo, it's a Woreda
https://en.wikipedia.org/wiki/Seraro) and migrate to Wuchale in northern Kenya.
According to the Gharri they chose to leave on their own after pressure from the Borana grew too great, though who knows, anyways they crossed over the Jubba into Konfur. After this, one branch of the Gharri decided to go back and reclaim their lands, but presumably your ancestors decided to stay behind and join the Raxanweyn.
The bit about being originally from the Red Sea Coast is probably close to true, though probably not the coast but rather the interior near Harar.