On the "Friend or Foe" question, I think we're supposed to come away with recognizing that both Marina and Penelope were in a situation where they choices were limited and both made some bad choices. In short, I don't think we're supposed to see either Marina OR Penelope as "villains" - we're supposed to have sympathy for them while also recognizing that they both made some pretty questionable decisions.
It's one thing I appreciate about the romance genre - they allow women to make bad choices, to sometimes seem "unlikeable," but also to say that even women who occasionally do the wrong thing deserve happy endings.
Marina's situation was bad - unwed and pregnant, with no prospects was definitely a bad situation for the era - but also, she was not without her own agency. She got into the situation she was in because of her own bad choices and throughout the series, we see her choosing to believe that she was entitled to get everything she wanted in her own way - child, marriage to someone she could love, a comfortable situation. She was definitely trying to deceive Colin and as he himself said, if she had actually told him, he would probably still gone for it. Now, it's understandable why she didn't - the risk was too high - but that doesn't mean she still wasn't trying to be deceitful to him.
Penelope was being guided both by wanting Marina to be happy - after all, she's the one who discovered that her mother forged the letter to Marina - and by her crush on Colin. To some extent, I wish that they hadn't introduced her crush on Colin as a factor, because at the end of the day, her actions were completely understandable if it were her just protecting a friend. But nevertheless, she did betray both her friend and her family, but she had also run out of options to stop a marriage that would have been built on a foundation of deception.
I don't think any of these characters are despicable - I think that they are human. But I am a bit surprised that people are casting Pen as a "villain." IMO, she's not, she's a character who was in a no-win situation who made a bad choice. That's true of Marina, as well, but neither are villains.