Rurikids, Umayyads, Karlings (in the main line), for one not mentioned yet the Guptas
I assume the topicstarter meant male line Habsburgs/Romanovs, not the Holstein-Gottorp-Romanov and Habsburg-Lorraine we had IOTL since 1730ies/1740ies.I'd go with either the Habsburgs or the Romanovs. Avoid WW I and they can easily survive. Contrary to what some would have us believe, these empires weren't ramshackle, tottering ruins destined to fall apart at the slightest push. They had potential to be much more. I also have a soft spot for the Qing. They could be saved if Emperor Guangxu manages to stop Cixi's coup and continues his reforms. Oh, and I almost forgot the Hohenzollerns. They were pretty bad ass at times.
Sigismund and Charles hated each other passionately. No way.Interesting POD will be for Zygmunt III to negotiate with his uncle to drop his claim on the swedish throne in exchange for the Northern Inflanty (Estonia) going to the Commonwealth.
And uncle and nephew will create an alliance between Sweden and Polish-Lithuania against Russia in the east and Denmark in the west. Sweden and PLC will kept Russia far from the Baltic Sea and PLC will let Sweden go after Denmark while in OTL Denmark was often Polish ally...
Shuisky were the only non-mediatized branch.Shuisky family (btw they still exist) was Rurikid, so I think would they keep Russian throne they would count as "Direct Rurikid" by virtue of being monarchs.
The House of Wessex, because its kinda nuts the number of times the house got deposed only to keep coming back, and itd just be cool for them to keep that up.
Surviving House of Medici would be intresting and change things in Italy. Would they eventually end to unite Italy, at least Northern Italy?
To answer your question. Yes, the royal house/Imperial dynasty has to be in a position of power, like the House of Stuarts continuing to rule the UK or Valois in France. That brings me to the other part of your question, as I'm aware that many people today have ancestral connections to these houses and dynasties. The goal here is to keep a direct line where they still have the name like "Valois, Tudor, Vasa, Rurik, etc", otherwise this thread falls flat as some of the current monarchs today (Looking at you UK) are descended from these branches.Do these royal lines have to still be in positions of power? Because I am sure there's quite a lot of people around the world today with ancestral connections to at least some of the dynasties listed.