Is it safe using 2 antivirus at the same time?

Nearly all AV programs have two parts. The first is running in the background all the time looking at whatever is coming into your computer (and sometimes, what is going out as well). The second part just sits there, like most applications, and does nothing till you run it to check a particular file or drive. It is quite OK to have more than one AV program installed SO LONG as you don't have more than one active at any one time. Usually, it causes little harm to have more than one running at once but it WILL slow down the PC drastically as each program tries to access the data the other is using and may even try to check the temporary and 'working' data of the other. The worst case scenario is that both programs will hang indefinitely while each tries to check the other's data and the computer will lock. Provided that you only run one program at a time, you can have as many AV programs installed as you want.