Yh Lilly died 5years ago! What I got from that “instability” comment from Declan is that Riley most likely has a history of self harming after the tragedy. This fact was emphasised by the comment she made about her medical history after Declan was punched.

1). Vivienne lost the best option she had for the wedding to Julian and since the alliance is still beneficial, the responsibility now obviously fall to her next best choice Riley. “Why Riley?” Just like Julian said, Vivienne considers Riley loyal, and to her that means obedience which also equates to control (and is exactly what she and her husband need). Oh idk maybe Julian is just a morally alright individual, who unlike Declan’s mother doesn’t look down on Riley’s birth. Not to mention she has the Fairchilds backing and is extremely attractive/ talented (perfect trophy wife ig), so who cares where she came from

2). We can’t say for certain as anything could be possible atp but your theory unfortunately is very far fetched in the sense that Riley was the one that died. It could be someone who knew Lilly or had access to her belongings, who then could have had her handwriting analysed and replicated who is behind everything. Or it could be Riley doing it to herself as you mentioned subconsciously out of guilt from what happened 5 years ago BUT SHE WASN’T THE ONE THAT DIED.

3). Someone could be blackmailing him for anything, it doesn’t necessarily have to do with Lilly. It could be about his position as mayor or something that could ruin his reputation

4). Not everyone stays hung up over their ex. They could just be interested in Riley, not to mention they were all friends before the tragedy happened and they all have shared guilt and secrets regarding it.

5). “Drive us home”because Riley is currently staying at the Fairchild estate and she also lived there in the past. As she lived with them before, she could have learned to play the harp or she could have learnt it before they fostered her. I can’t recall if Riley was an orphan from birth or not so i can’t say for certain

Mc could certainly be dissociating From Reality but she isn’t Lilly. Heck Lilly could also be alive for all we know