Cain's official fiancees are Telestia(princess), Silk(duke's daughter) and Tifana(technically elf princess/duke's daughter as well). Meanwhile Hinata's engagement to him is still being worked on between the two countries due to Hinata being a Saintess, her country doesn't want to give her up yet, and Cain being a noble his country wants to keep badly. Though it's heavily hinted that it will probably be official at some point due to the whole oracle thing Hinata pulled.
Cain's next official fiancee is actually an imperial demon princess by the name of Lisabeth van Benestos who he saved during this arc. The demon "world" or their country the Benestos Demon Empire is a bit more complicated here. She's the daughter of the Demon Emperor, while Seto is one of 4 Demon Kings that were assigned due to their strength. Their country is pretty much a big threat even without relying on the Demon Kings because demons are actually very strong in magic and even a single demon can cause quite a lot of damage on their own. The only reason why Lisabeth was in trouble in this arc was because her older brother has taken the role of ruling as Demon Emperor due to their father being bedridden, and due to her brother’s attempt at trying to marry her off to one of the Demon Kings, she ran away from her country which led to her being captured. They used a magic suppression choker on her to prevent her from using strong magic. She was caught due to a mistake on her part, her disguise magic stopped working when she fell asleep drunk, and was later used as an attraction via a fight to death against another S rank adventurer where her magic was suppressed, this is when Cain in disguise saved her and teleported her to his place in Drintor for safety and rest, Darmeshia knew who she was and basically sorta suffered not being able to say anything until the next arc.
Cain's engagement to Lisabeth is officially recognized as part of a peace treaty/alliance treaty after Cain helped prevent a war between the demon country against all human countries. It almost happened due to Lisabeth's being captured and almost killed for an attraction was found out earlier by the demon country which enraged the country at the news and incited most of them to want to go to war until Cain intervened at Lisabeth’s request.
Now the reason why Lilutana can't be one yet is actually due to her country, the Baisas Empire doing some plots behind the scenes. In the current arc of the WN, the Baisas Empire assassinated the pope to steal some special items, those special items are used for summoning heroes. They summon 4 people, one who is a Hero, one who is a Sage, third I am unsure and the fourth is a normal person. They use the Hero, the Sage and the third summoned to send them against the Beast Kingdom, which Cain gets involved in as a healer due to the fact he is STILL underage at this point.
This is where the WN has slowed down. This is just my theory crafting at this point, Cain may gain several more fiancees after this arc is finished. We're looking at possibly one Beast Kindom princess due possibly having fallen in love with Cain's overwhelming strength just similar to how demons view strength as right, Lilutana for the Baisas Empire as part of some peace treaty or something like that, and this last one is only based on one WN chapter from very early at the beginning but it could possibly be one of his old friends from his past life where she's the Sage and her little sister is the normal one, who he saved before dying from being stabbed. In that early WN chapter, it's like heavily hinted that she had feelings for Cain's past life and she may end up confessing to Cain once she finds out who he is.