There is a proverb in Russian:"за двумя зайцами погонишься - ни одного не поймаешь"? (if you chase for too hares - you will not catch a one). It means, that it will be very difficult.
I'm also trying to learn two languages at the same time - English and Chinese. The first one I have been learning pretty long time, and already know "something" :))) (B1 level, if to believe the results one of the language tests on the Internet), the second one, Chinese, I have been learning less time.
From my own experience I can share some of the techniques. For example, if I want to study some topic in English, that first I make a list of words, phrases, which are necessary for this in my native language. Then I find a translation for the whole list in different English dictionaries.
But,... Why not to use all the same list and not to find it's translation into a second languange I'm learning - in Chinese as well? As in Chinese I'll also have to communicate in this same topic!
Thus, I, have made one list in my native language and then translate it at once into two languages I am learning. And, thus, "I can catch the both hares", i.e. to learn two languages simultaneously.
Here it is important to have for each of the languages it's own copybook, text file, programs, etc., in which would be recorded all new words, phrases as well grammar rules.