I need some advice, please (POV)

You could alternate between 1st person POVs with both of the twins, and just make sure the reader knows who's who by putting the characters' names as chapter headings or somesuch.

 

Hmmmm... Just on the information you've provided I'd say third person. The choice of going with twins is often a desire for symmetry or duality. A first person perspective places a heavy emphasis on the view point character. That weight risks unbalancing the symmetry / duality of twins.

 

One thing I've noticed with several of really good authors is to just switch like Ireth said. A lot devout specific chapters in the perspective of a single person, alternating between those they want to tell the story through. It is very effective and gets you in a good mindset for everyone involved.

 

As far as switching goes, one method I've seen has each perspective written with a different font or one written in italics, but I don't know how well that would work with longer periods devoted to each viewpoint.

 

I would thoroughly outline the book in third person, then write your first draft in first person alternating between each character. That way you can get down what happens before concentrating on how people perceive and feel about what happens. It's likely that during the draft you'll discover that how the characters feel might make some of the actions outlined unlikely, which will be generative, the story taking on a life of its own.

 

I would definitely suggest writing your first couple of stories in whatever language you're best at. Having to worry about grammar and word choice in a language you're not completely comfortable with is another hurdle on top of all the other hurdles a writer has to overcome. That said, if it's just for fun and if you want to get a better handle on the language then that seems like a fun and useful method to get a better grasp of the language.

 

Is it possible to tell the story from a different character's POV? Like the cat's? Or some character that can easily and believable switch from being with one sister then the other? If not then I suggest a method that's working very well for me (I had the same problem), write a piece of the story in a different format. Verse, screen play, stage play. I strongly suggest the latter two as they help to keep you at a better distance to truly see each character and the story in greater depth.

 

I would write about five pages in first person, then try the same five pages in a close third person. I find first person a little easier and it often flows easier when I'm onto a really solid idea. Don't be afraid to switch the pov, but break the book into parts/sections, not just chapters. Make it clear in the first line that you are switching.

As for the language, I would go with whatever you speak most. I read and write French fluently; I would not even consider writing a novel or short story because I don't see and hear it every day.

But, you could choose to write in first person and write in English, make it a feature of the narrative, slip in some of your native language now and then. I say things in French without realizing sometimes, and there are ideas that I can convey with one word of French that requires an explanation in English and vice versa. That can really draw in the reader.

Have fun!

 

As a first person-person, I say try it. I have only ever written one novella with third person POV and it has its pros and cons as well.

 

I'm a fan of Deep 3rd, though I've written in 1st when the story called for it. A story about twins would be tough to do in first without you and/or the reader getting confused, I would think.