Younger son got Rikudou's physical energies, which gave him longevity (life force), large chakra reserves (stamina), the body power (most likely mokuton and other yohton releases), and of course this comes with the bijuu control/suppression abilities.
So there must've been a split in the lineage few hundred years later. The uzumakis chose to seclude themselves onto an island, in order to preserve Rikudou's fuuinjutsus, and they chose to be less combative in nature, concentrating on seals in order to still support their brethren, the ones who remained onto the mainland, the senjus. So the uzumakis are just an offshoot of the same lineage from the younger brother. They are one and the same, just living in different places, both possessing the strong physical energies of Rikudou, both possessing the will of fire, yet the abilities/traits of the younger son, manifested differently between the two clans, depending on what they chose to concentrate on. The senjus had a greater will of fire, cause of their need to constantly fight wars and need to endure, to protect their clan and allies. They were more combative thus, had a greater need to protect the ones they loved, thus a greater will of fire. The uzumakis had the longevity or long lives, and they kept the sealing knowledge of Rikudou's fuuinjutsus. Both senjus and uzumakis got the large chakra pools tho. However only senjus were more dominant with the body power, this would include mokuton and other various yohton releases related to the body. And certain uzumakis with strong energies were able to use chakra chains to suppress bijuus, and seal them. The physical energies of Rikudou were present in both clans, as both are split lineages of the younger son, however the physical energies manifest powers differently in each clan depending on what was needed.
Mokuton is far more versatile in combat, yet also retains a bijuu control ability, however is unable to seal completely. The chakra chains are helpful in bijuu suppressiong and the fuuinjutsus seal the bijuus into jinchurikis. All the powers are related tho, as they are all life powers, or yohton (yang) releases of Rikudou's physical energies.
Hope that helps.