I don't agree with Lidia at all, in my opinion it's better to learn from different groups. 

Learning Italian, Spanish and Portuguese at the same time won't make you speak any of them, it'll be a huge confusion and mixture and at the end. Mixing languages is disrespectful in my opinion. 

I learn French, German and Russian at the same time and practice my current ones (English and Spanish). The only thing is that you need to share time with them which will make it a little bit slower. 

Well, those 3 languages aren't even in same group. If you deside to do that, it's better to learn languages from same group, like for example " Italian, French, Spanish" or like "Polish, Serbian, Russian. English, German, and French are only simular with international words, but international words are often used in any language. Example.. "radio, tv, vine etc etc. Good luck, anyway..

@Lidia, sure, it's just opinion! I just shared my opinion because it is my own experience and the experience of many other people that I know and especially my students who already speak other similar languages and now try to learn portuguese, they have a hard time seperating the languages. I can guarantee you, it's hard to learn two similar languages at the same time unless it's okay for you just to mix both languages thinking that everything's fine and everyone's understanding you. Just for the sake of communication, ok, you are completely right, but if the person's goal is to achieve fluency and truly speak the target language, then it's better to prepare psychologically a lot before trying it or I would suggest to learn one at a time! 

I agree with Gerardo. It's very important to train everything that you learned.

The most important to learn any Language is to practice. If you have time to learn or more Languages, Fabulous! However, the dedication must be continous. You must write words, speak and listen the Languages all the time. Regards!