Is it wise to learn multiple languages at once(same time)?

It's neither wise nor unwise. There is certainly nothing against it, and many people see a positive advantage.

Like John P, when I was at school we learned French, Latin and Russian all at the same time. Later I added Greek, so for one year I was learning four languages.

Not everyone did this; it depended on our various aptitudes. I showed none whatever in the sciences, so while my friends were doing maths, I was learning Russian.

At school (all those years ago!) I was learning French and Latin and German at the same time.  It seemed the normal thing to do at our school.  We had a choice of not doing 2 modern languages and doing something else.

There's nothing wrong with it. In Atheneum (dutch "grammar-school"), I had English, French, German and Latin in the same year

What would be smart is learning some Esperanto *before* learning other languages.

See wikipedia Propaedeutic_value_of_esperanto

Depends on the languages and how much you use them. French was my first language .. when beginning to learn English focused on that. I found Spanish easier though because 

of its numerous similarities with French & now speak all three on a native-speaker level.

Over the years, I've managed to learn the basics of several others, but don't use it much. 

Learning two languages at at the same time really stretches your mind. Although it can be difficult, having to frequently switch back and forth between new languages challenges your brain and hones your language learning skills such that learning future languages is faster and easier.

It really depends on whether you are good at languages or not.