There's a horrible misconception that you need need to do mental gymnastics like allowing Manus date but not publicity etc. None of this shit matter in the slightest. Here's how it works.
- In your background choose that you love Lena and spend time with her.
- Accept Vina into your council
- Completely support her relationship with Manus
- Always be nice to her
- When it's time to finalize her marriage arrangement, you must say "I have someone else in mind"
- In that dialogue tree, always be nice to her and tell that you'll respect her wishes at the end
She will accept whoever you're suggesting. That's it