Sigh... I did not bother before.
The trouble is there are only really a few relationship scenario's that count when consideirng Ranma/Tenchi crossovers due to reasoning of almost all the authors.
- Ranma/Jurai no relation. And thus no connection to Jurai. Benefit is Ranma has earned all his skill and it is not dependant upon genetics
- Ranma/Jurai relation. And thus connection to Jurai. This is done primarily by making Nodoka another daughter of yosho. But variations exist, including Ranma being a reincarnation of a offspring or a offspring of the Coushin, generally Tsunami, sometimes Washu, and at least twice, Tokimi.
Yosho, Achika/Kiyone(depending on continuity), and Tenchi all have the House of Jurai or Jurian royal powers. So he could not be directly related to any of them and meet your requirements.
Now... If he is related to Tsunami, he also gets the jurai power, but is no longer directly related to Tenchi. Likewise any Jurain of clan Masaki backdrop gives him relation to Tenchi in the greater scheme of things. Thus none of them would meet your requirements either. Any other Jurian noble would not give relation to Tenchi, so they are out as well.
Washu, Ryoko, and even Mihoshi could not meet the requirements. Kiyone (partner, not Tenchi's mom), would also not meet both the requirments.
If Ranma is related to Tenchi, and not have Jurai connection, then it simply has to be through Nobuyuki. I'm only aware of one such story. Where Nobuyuki and Genma were brothers or cousins.
Nobuyuki and Genma are cousins in:
R-MULTI 'Life and Times' by Donny Cheng - [Status=Not Complete] - [Last Dld=01/29/2002] - [Size=531kb] - [Files=20]
Another exception... but does not meet the requirements. A blood transfusion gone wrong makes Ranma related to Tenchi, yet not officially endorsed by Tsunami until after the fact. That is in:
R-MULTI 'The Light Hawk War' by Chaos Lord - [Status=Complete] - [Last Dld=06/02/2004] - [Size=892kb] - [Files=12]