Parents die>all staff leave ( lack of $ to pay them, I presume)>(no family show to take him or adopt?, No family try to move in or take the state from him?) New maid shows and got hired(at this point I think said maid is paying little master for the privilege of work for him and secretly funding the state expenses)>Maid die of an specialy embarrassing comment made by little master> with no $ left to maintain the state or pay taxes, little master start to live in the streets and dies shortly after> they are reunited in the afterlife and is maid victory because she can't die of embarrassment anymore>the end.
Alternatively, they're here to contain his chad powers to avoid all that pure energy being contained within one woman, which is potentially dangerous for her health.
I think that the new character is there for some kind of status report, either because Lilith is in training or perhaps it's for Lilith to give some kind of update about Yuuri's well-being and education. One of the biggest mysteries about Yuuri is his education
(unless you subscribe to the theory that it's a haunted mansion and Yuuri is the ghost, having died of illness and/or neglect at some point after his parents died and the servants left)
. I suppose he does school remotely, since computers seem to exist, and for whatever reason he's deemed intelligent enough to not need any tutor, but they probably need to do in-person check-ups with at least his legal guardian from time to time, and Lilith somehow seems to have assumed the legal guardian position.
@lesseffective Volume one of the tankoubon unites the web version of the manga and the serialized Gangan Joker version into the same timeline (which Wakame Konbu probably always meant for it to be anyway), so it's well past the point where Yuuri found out her name is Lilith. He also said Lilith's name in the previous web chapter.