Mask of Deception (2nd Game): https://vndb.org/v7721
Mask of Truth (3rd Game): https://vndb.org/v18717
Completely linear
Only the original Utawarerumono is 18+
The Remake of the 1st, and the 2nd and 3rd Games are all-ages.
Constant Strategy RPG gameplay
Utawarerumono's strongest point is probably its characters. The games are really SoL heavy, especially the second one, but I haven't found that boring even bit. That's precisely because the characters, their interactions and relationships with each other are increbidly well-written. Even if they're mostly not that complex, they're still vastly enjoyable. Coupled with a great worldbuilding, nice art, and excellent music it makes for a great experience. While the story is not extraordinary per se, it's definitely not bad and has it's own great moments, mostly in the latter games.
Prelude to the Fallen Steam - https://store.steampowered.com/app/1151450/?utm_source=vndb
Mask of Deception Steam - https://store.steampowered.com/app/1149550/?utm_source=vndb
Mask of Truth Steam - https://store.steampowered.com/app/1151440/?utm_source=vndb