Best way to learn
Which is better? Learning 2 other languages or 1 other language at the same time?
I'd suggest learning one language at a time, and if you have a plenty of time, dedicate it to reading in the language your learn, to listening to podcasts, communicating with native speakers, etc. It would more efficient than learning two languages and only doing exercises.
Just do what you want. If you have the motivation and the time you can learn as many languages simultaneously as you want. Some people can get confused if the two languages are similar (eg. French and Spanish), but that usually only happens if you're a beginner in both. So it might be wise to pick two unrelated languages, or wait until you get one up to intermediate before beginning a new one.
I'm learning two and it's no harder except in the amount you need to remember and the extra time involved. School kids do it all the time.