I’d start by checking the float level first. Did someone replace the carb with one that has the idle jet one the side of the carb? If so that could also be plugged, resulting in the same condition.
This is my uncles mower, all I have for 2 stroke oil is stihl hp ultra i use for my chainsaw , is it ok to use this with some fresh gas to see if that is the problem?
Yes, 2-stroke oil is 2-stroke oil. Modern Stihl oil is probably much better that the old petroleum based stuff from the 1980's he might be still using.
If there is one of those priming bulbs that you push to pump fuel to the carb, then make sure you pump it enough to flush out all the older fuel. Also check that the old fuel hasn't fouled the spark plug.