Hold on... i think this is where people are getting confused.
Katagiri is 100% Quincy but she is pretty much part of a mutt family. Her blood is that of several families.
Ryuuken is 100% Quincy but a Pure Blood because their blood as stayed within a region. (had to think of a proper way to say that because i believe they mentioned Katagiri as a cousin to the Ishida family)
Isshin wasn't Ichigo's real father. It's going to be revealed that the Hollow attack somehow created a life force in Masaki which absorbed Ishhins Shinigami powers while Urahara had him save her. Since hollow are not human they have no blood type which leaves Ichigo with pure Quincy blood and Shinigami and Hollow spiritual power.
Look at the Zanpakutos for example, Zanpakuto have unique ability right, but Ichigo's was a copy of Isshins as far as abilities go. Granted we never see any other familial zanpakuto relations but a father and son should not have the same zanpakuto ability(Getsugatensho) Which makes me believe they are trying to convey that Ichigo only got powers from Isshin not actual DNA.
Isshin is Ichigo's father
-Conceived 5 years after the incident (he is 15-16 now, incident was 20 years ago in the bleach timeline).
-Has been mistaken several times to look like Kaien (Isshin's younger brother) Can be a common family trait.
-Ichigo's sisters both have residing powers as well, though not as strong, its proof enough.
As for the Zanpukto, its pretty much already been said in both cannon and non cannon story line that having 2 similar zanpakuto's is extremely rare, but possible. Yes Ichigo's was manufactured by his inner hollow since he was born of 4 equally divided unique souls. Ichigo has his own powers, he has yet to awake all of them. thats been the progression of the whole story. He awoke his Hollow and Shinigami powers on his own after Byakuya cut them from him when they took Rukia away. Those were his own powers, he never lost those just made them go dormant because he has so much inner power its not even measurable (reference when he scarred the Menos Grande in KT with Isshida and Urahara, Urahara says his power is so vast its like opening a faucet full on, its like a dam, once opened full blast its extremely hard to close). When they gave him power to fight Ginjo, he already had a lit match, they just added fuel to it.