Is it safe to extract four wisdom tooth pplus 2 infected premolars at once?

This depends on your physical and mental health. Are all the wisdom teeth fully impacted?, are you in good health, and not on any medications?, will you be getting IV anesthesia?, the oral surgeon will advise you what is in your best interest. Your health is important not how many teeth to extract at one time.

Safe, yes, especially when done by Oral Surgeon. Note that leaving infected teeth in place is harmful to all of your other organ systems.