That was my thought but i couldn't explain exactly since i suck in English.
When i played Lalya route her mom Ana warned her what unprotected sex can bring to her and that she gave birth to Lexi when she was 18 or so. At the time she was roommate with Emily, perhaps she already gave birth. That one scene when Mel was explaining history of Emily and Santi we could see Ana showing up without being pregnant or she carried it in early stage. And since incest is something that's already excluded from this game the question is who's the dad of Lexi and Layla? Is Santy in any case conected to Ana and her daughters? Like if we presume that he's not bioconected to L&L, is he their stepded? All we saw byfar is Santi's pic on wall at Gabi's place and mistery man at Ana's place.
It's really confusing right now and Nyx really knows what she's doing by leaving us to speculate.
In the restaurant scene Adriana explains she didn't stay much at the dorm because she would stay at her parents house taking care of Alexis, so in the Emily flashback we saw, Alexis was 100% an infant already, just like Melissa already had Erynn.
In fact Layla is the same age as the MC, in that scene Alexis is already born and Layla might be in the oven(or will be shortly).
I don't think there's any connection between Santi and the Monroe family, just too convoluted a story... even for this game lol
We don't know anything special about Mr Monroe, there have been no info on him(Navarro is the one that gets constantly name dropped).
Nyx just has a weird fetish of keeping Monroe hidden or shot from the back for no discernible reason so far, maybe because people confuse him for Navarro.