In addition to the excellent thoughts by OP above, I want to add on about the reason behind both Khun Yai (in 1927) and Kanthorn was born sick, and how that relates back to Commander Yai, which is why fans desperately NEED a season 2.
Khun Yai said he was born sick so his family had to make the blessing ceremony to try and bring his "spirit" or "blessing" back to him.
2023 Yai Kanthorn was also adopted because he was born prematurely and sick. His real mother is Ueam Dao (Khun Lek's youngest daughter) but his aunt Ueam Duean (Khun Lek's oldest daughter, Khun Yai's favorite niece) had adopted Yai Kanthorn so he got gradually better in health.
Point is both future reincarnations of Commander Yai were both both born sick, missing their "blessing". So why is this the case?
We can trace back to the words in the final chapter when Commander Yai was in a life and death battle and before he sacrified his life in that battle, Commander Yai made a promise to Jom.
"Jom-Jao, listen, though you are fated to be apart from me, my love will never fade, and it will follow you like a holy spirit, protecting you in my place. No matter where fate brings you, no matter the danger you encounter, may those misfortunes fall upon my spirit instead of yours."
To give some context, you can see the blessing ceremony being mentioned again in EP.12
It's an ancient belief among some northern people. They say we've got 32 blessings, which will protect us and bring happiness in our lives. When we get sick or undergo misfurtune, as you did, we should undertake such ceremony to bring the blessings back to you again. But when we die, our blessings will be reincarnated in the form of our close relatives. That's why when a baby is newly born, they tend to guess who it was in the past life.
You can see that because of this promise, Commander Yai had traded his "spirit"/"blessing" for when Jom had crashed his car into the river but did not drown, miraculously surviving -> resulting in his future reincarnations (Khun Yai and Yai Kanthorn) to be born sick with missing "spirit"/"blessing".
So when both 2023 Yai Kanthorn and 1927 Khun Yai meet Jom, they feel like they're finally "complete".
The dialogue in this scene in EP.10 is also evident of Yai's completeness after meeting Jom. The translation isn't able to do it justice but Yai uses "kwan" and "por jom kwan kong shan" which is both a play on word of the "spirit"/"blessing" and also "jom kwan" = my dearest jom.