Top 3 names 🩷

I think they all lovely names.
Maybe also take the initials with your surname, and see what the acronym lands up being.
Write then all out, fully with the middle name and surname, stick them up somewhere you see. And get a feel for them. Also you can pick when you meet your little one, see wait suits them.

I'm not a fan of Heidi, personally, as I find it a bit twee (hi-di-hi campers!). It's definitely the best match with Orla though.

Lana, even without the issues of what it spells backwards, is too similar to Orla, given that they're both 4 letter names with 2 syllables and repeat the end sound. Visually, Orla and Lana are too similar, as well as when said aloud. Going back to the 'anal' issue too, I know you say it's not an issue but when you consider you already have an Orla I think it could be major teasing potential for them as a pair when they grow up. They'll become the oral and anal sisters. Sorry, but teenagers can be really cruel.

Olivia is lovely, despite the popularity, but again it is too repetitive. I would avoid the same initials, especially as the end sound is also repeated.

So Heidi is the only one which goes. Orla and Heidi are fine for siblings.

I like Heidi.
Olivia is too popular for my taste and someone once pointed out that Lana is anal backwards and now I can't unsee it.