That's so time-consuming, pains-taking for basic learners. I've ever tried to learn Spanish and French at the same time before, I got tired of understanding two different basics at once after all. I don't know what I've thought when I tried to learn the two. On the flip side, I've been learning English and Japanese and haven't had any problem to learn the two. I think two reasons explain why. The one reason is that I've reached an intermediate level(or semi-intermediate) in English when I got start to learn Japanese. The other one reason, is that Korean and Japanese are typologically quite similar, therefore I got a head start. Japanese grammer is getting difficult to understand for me these days though. I'm still working on perfecting these languages and consider to get start to learn German.

yeah i used to learn english and french at the same time, as a result sometimes i read english in a french way...

It will be very confusing, especially if you are learning two different languages that have different grammar structures.

one at a time. but this is comming from someone thats trying to learn mandarin and japanese at the same time haha. xD