I have to agree with this one. The family trees seem to produce a bumper crop of nuts when they produce at all.
I have been very disheartened by this and every attempt on my part to prevent poor traits has failed. It is very much like a contagion, once one family member gets poor tax man or the dreaded trait of tax-farmer(different from the ancillary)they all try to out do the others until you can only use them in ambushes or send them on crusades. They come of age with terrible traits so that you have to keep a close eye out for any showing up in towns.
It is too bad I didn't make any screen shots of some of the family trees near the end of one of these games. The abundance of Wall-nuts was astounding!
Most of them are mad as hatters, extravagant to the last degree, of practically no military value, and with no religion what so ever.

Not being able to swap ancillaries is only a very minor problem. I don't know why CA decided to make all the royal houses of Europe into such degenerate swine but it seems certain that they will all turn out that way. Even those adopted can only be left in settlements for a few turns before they are totally useless...and I never have large sums left in the treasury!!!! What triggers all of these pathetic traits in the first place, and what am I doing wrong never to get any positive traits passed along???