Can we make a conditional switch in blynk mobile app i.e. If we want to Turn High the BUTON1 only when either of BUTTON2 or BUTTON3 are HIGH. ?
It is easy to use flags in your sketch 
Yes, this is possible. It’s called “Rule Engine”. It doesn’t have UI right now, so it is available only for the White Label clients. So for now you have to do that in your firmware.