Trying to figure out how I am related

[Dsiems]

My birth father is unknown. When I submitted DNA on Ancestry and on 23and me I got a close relative on each. Both were showing as 1st cousins. Here is the problem. One is the grand nephew of the other. Below is the scenario with initials of each person
Trying to figure out how this is possible.  Any help understanding this would be greatly appreciated

Possible Father-NAB deceased

1/2 sister of NAB and JHB Full sister of PEB-TAM
TAM’s son JOM showing as my 1st cousin 14% DNA across 27 segments

Brother of NAB- JHB Close Family–1st Cousin
Shared DNA: 1,892 cM across 75 segments

Other possible father deceased PEB 1/2 brother of NAB full brother of TAM

[avm228]

Welcome

I am afraid I didn't find this easy to follow.

TAM is a half-sister of JHB?

So isn't JOM (son of TAM) a half-nephew of JHB? You said grand nephew.

[Craclyn]

The possible relationships at 1892 cM are grandparent, grandchild, aunt/uncle, niece/nephew or half sibling.

[Gadget]

I agree with Craclyn. For example,  my niece and I share 1846 cM across 75 segs. Her son and I (my great nephew)  share 1100 over 49 segs.

This should help with possible relationships:

https://dnapainter.com/tools/sharedcmv4


Gadget

[Dsiems]

Thank you that would make more sense. JHB thinks he is my uncle not my cousin. Is there any way to calculate the cM from a % as that is how 23andme reports it.
If JHB is truly my uncle, and JAB is my father, then TAM is my half sister and JOM would be my nephew. Would 14% across 27 segments support this?
(Father)                                                        (half sisters)
NAB                ME(diff mother)    CSM           DST        TKM      KLM
           Children                                                         JOM (showing as first cousin but should be 
                                                                                          nephew               
Siblings (Uncles)                                              Children (1st cousins)
JHB (showing as 1st cousin but could be uncle)     JHB   KDB   SJB   MAB

1/2 sibling different mother
PEB

[brigidmac]

That looks very probable
My aunt shows up as first cousin degree of relationship but once. Mutual trees are made relationship is given as aunt

Some probable 2nd cousiñs were actually believe 1st cousins with only 1 grandparent in common so half cousins

Good luck getting to the truth

[Gadget]

It might be worth looking at this link

https://isogg.org/wiki/Autosomal_DNA_statistics

and scroll down to the table headed:

Average autosomal DNA shared by pairs of relatives, in percentages and centiMorgans

This will show the approx/probable  % and cM equivalents for various relationships.

Gadget

[avm228]

If you do DNA comparison between you and your match(es) in 23andMe it will tell you how many cM on how many segments you share (and paint the segments onto the chromosomes).

The “view DNA comparison” link is on your match’s page, under the % shared - follow that link and you can compare yourself with multiple matches simultaneously.

Some people opt not to share that information until you connect with them.