Syaoran (Tsubasa) and Sakura (Princess Tsubasa)
...for those the time stopped...
These two have a specific connection with Yuuko.
First thing you should know is that the storyline is really complicated when it comes to them and the main point is that Yuuko saves Real Sakura’s body from Fei Wong, while the later takes Real Syaoran and Sakura’s soul creating an alternate universe where he places clone Sakura and clone Syaoran to use in his intent of reviving the witch.
There is not much interaction between real Sakura and Yuuko; so there is not much to write about, just that Yuuko feels the need to protect her and not only because Fei Wong keeps creating paradoxes and similar but also because in the end she came to care for her and her well being.
There is some interactions between Real Syaoran and Yuuko; the first happens when he is 7 years old and appears with his first wish; which Yuuko grants for the price he will never see his parents or his world again.
Second time they encounter is the second wish by the real Syaoran and it’s price is his freedom and the connection to his parents. This is the time he gets kidnapped by Fei Wong along with real Sakura’s soul and when Watanuki is created to take his place in Japan with real Syaoran's parents...
Third time when they meet is when finally the time for Shaoran is to go on the journey he payed the price for. To save real Sakura. In that moment he also pays the price for the incident that Watanuki will have.
Syaoran and Watanuki are one but two different entities; Yuuko has taken great liking to Watanuki and I think she also has an attachment to real Syaoran because the two are the same, that is also one of the reasons why she probably keeps helping him aside the fact that she wants to keep the balance that Fei Wong has been trying to overthrow just to prove himself more powerful than Clow.
These are all mostly speculations; while there are interactions between them, there is nothing sure; especially when it comes to CLAM and their paradoxical ways of creating their characters and their worlds.Also I am almost sure that Yuuko has a soft spot for troubled children like the two Tsubasas are; and that she likes to help when it is for the rightful cause even if she does always asks for a price; but that’s mostly to keep everything balanced as it should be.