Thanks, Rata. But I think you missed the requirement in the OP that uncle/aunt by marriage doesn't count.

> > > "Direct" means blood related, i.e sibling of one parent, not "uncle by marriage".

In hindsight it becomes clearer why breeding dogs would be a better setting for this puzzle.

Dogs don't know marriage, divorce and soap operas° ... ;)

And many breeders rely on incest, restricting them to uncle/aunt relationships would be a "moral" advantage.

Update

The trivial solution (of many) if "by marriage" was allowed ...

°)