Your challenge is if you choose to accept it is this:
Has anyone else noticed how much more regularly the varying branches of the house of Bourbon marry amongst each other (including those lovely uncle-niece matches)? Not only that, but for the most part, they seem to be unaffected by this.
In the space of four generations (Louis XIV to Louis XV/Carlos III/Filippo I), the Bourbons ruled not only France, but Spain, Naples & Sicily and Parma, too.
In the space of four generations (Maximilian I to Philip II/Maximilian II), the Habsburgs acquired Burgundy, Spain-Naples-Sicily, Hungary-Croatia-Bohemia, (temporarily England) and Portugal in addition to Austria.
The Bourbons flourished between 1700 and 1900 in spite of constant intermarrying between the branches - including uncle-niece matches.
Between 1500 and 1700 the Habsburgs lost Burgundy, Portugal, nearly Naples and finally Spain (plus almost losing Bohemia, and then winning back Hungary only to nearly lose it again)
with constant intermarrying between the two branches - including uncle-niece matches.
Thus, the challenge is, let the Habsburgs survive in like manner over 200 years (1545 (birth of D. Carlos) - 1741 (birth of OTL Josef I)).
Points if by 1600 Burgundy and at least one other royal kingdom besides Spain is under male-line Habsburg rule.
Bonus points if that lasts to 1700.
Extra bonus points if it can last to the present.
NOTE:
Karl V is not allowed to marry again or have any more sons than Felipe II survive (otherwise it wouldn't be much of a challenge now would it?

).
And the Habsburgs are not allowed to inherit any new territories nor are the thrones of one of the cadet branches allowed to be in personal union with any other throne (i.e. Spain-Burgundy; England-Naples; Austria-Burgundy etc.)
(Austria+Hungary+Bohemia is the exception)
While this
may be a Habsburg wank (not really sure, since they controlled all of those territories OTL

), it may
not be a screw to any other country (England, France etc).