how many novenas can you pray at the same time? like example to different saints at the same time?
As far as I know, there is no "rule." Personally, though, I wonder if it's a good idea to do several novenas at once. It seems more effective to focus on one at a time.
There's no "legal" limit, but prudence would dictate that you not overdo it.
Certainly, you would not want to bog yourself down with so much vocal prayer (saying prayers written by other people) that you leave no time for mental prayer (speaking to God from your heart and listening to Him), which is much more important.
It has happened to me that I had started one novena for my own intentions then someone asked me to say a different specific one for their intentions, so in that way Ive had two or three going at the same time. I dont think its necessary to say several different novenas for the same intention or person though thinking that just in case one saint is busy or not listening you should ask several Trust me one will hear you!