can i mix octane 95 petrol wif 98 petrol into a vehicle without any adverse effects on the vehicle?
Sure can mix, don't worry.
I haven't mixed 95 with 98 before, but read on papers before that its okie, as long as your engine octane specified minumium 95 and above or 92 etc.
I mixed V-power with 98 and got no problem with it.