Six SOULs [DT]

Asgore and Toriel are Boss Monsters, so they're obviously alive, and if Alphys and Undyne are also alive, it means they must be in early childhood/teens too, if "a long time" passed between the six's arrival and Frisk's. However, Alphys only became the Royal Scientist by "creating an artificial soul" (though really just giving Mettaton a body) long after Gaster's demise. And even then, it took a while before she did her experiments with Determination, thereby creating Flowey and the other amalgams. If that is the case, how is Flowey already present?

Other questions that occurred to me are:
1. Who is the current head of the royal guards?
2. All the teenagers in the original game are children or unborn, and the adults are now teens, so do we need to make up our own monsters?
3. Have Napstablook and Hapstablook appeared yet? I assume their family still controls the snail farm and that they still get regular customers.
4. Do you have replacements in mind for the unavailable main characters?

The children meet Toriel in the ruins just after she abandons her husband. This is because she is disgusted that he has declared war on humanity. After they convince her to let them leave, they head to Snowdin Town.

In Snowdin, they encounter a young Grillby. Grillby befriends them, but after seeing some character's genocidal acts, decided they threaten his home, and he challenges them to a duel. When they spare him, he realizes he was wrong and let's them go.

They proceed to Waterfall, where they encounter Paws, the fluffy white cat that is lieutenant of the royal guard. And he wants to kill them. They spare him, before heading onward. They encounter Dummy, defeat him, and head to the Blook Family Snail Farm. They leave shortly after.

At the end of Waterfall, they meet Killa, head of the Royal Guard. She fights them because she was ordered to, but she doesn't truly want to. In the end, she cannot kill them because they remind her of her young daughter, Undyne. They are spared.

They head to Hotland, we're they meet Gaster and his apprentice, Alphys. Gaster explains his studies of the time travel and space travel, and how he is creating a machine to do those things. He says it has not worked, but he intends for it to connect to separate points in time. Unaware to him, it has worked, and that was how the group encounter a Flowey. They met him through a rift in time. And accident then occurs in the Core, and Faster is spread throughout time and space. The group leaves.

They go to Judgement Hall, where Gaster uses the last of his energy to make a physical being. He judges them, they fight, and he is defeated. They then go to Asgore, where they are killed.