hp research query the 78th: the blacks?

So, my question on Harry's untold riches threw up a number of subsidiary questions and the one I am most interested in at the moment, for various plotfic reasons, is:

What are the exact family relations within the Black family?

Both Sirius and Narcissa & co are called Black, so presumably they inherited the name through their fathers (given ye olde wizarding laws of prediluvian non-equality-in-marriage date). So we have two Messieurs Black marrying... whom? Who are Sirius' and Narcissa's mothers?

And which one of the two Black brothers (who are Sirius' and Narcissa's dads respectively) is the elder? saeva says that Sirius' line of the family is the 'main branch': how do we know that? Is Sirius' father the older brother?

Are the two Messieurs Black even known to be brothers in canon?

*stares at own sketchy pencil rendition of the family tree*

Note: I am not interested in interview canon. Book canon only!

Though, ahem, I am, of course, not interested in any canon whatsoever... *whistles innocently and runs away from lazlet and helenish*

new pigs!

Today I bought two new guinea pigs.

They are female, and the children have called them Meggie and Polly. Meggie is a tiny chestnut runt of the species American Crested, and Polly is a fluffy, beige-white big mamma of the species British Rex. She looks like a miniature sheep.

They are still very nervous and not making any of those cute squeaking noises. They also don't have the cute tufts that the eaten guinea pigs had, and they are not siblings so don't cuddle up to each other.

*tries to stop investing too much emotional energy into pigletdom*

The children are very happy!