Re: How would you choose twin names?
I would choose based on which order rolls off the tongue more easily.
For example, Maren & Rosa sounds nicer than Rosa & Maren because the consonant ending helps to avoid blending with the and - making it sounds more like "Rosan" than Rosa.
Also, if one name were shorter & simpler, that name would go first. I.e. in John & Oliver, John would go first so that it doesn't sound like an afterthought to Oliver.