When performing ghusl, is it permissible to wash the body together for example. If I am washing my body while it’s under the shower- Is it enough for the flowing water to just flow to all parts of my body together at once e.g. if my hand is washed when moving it under the flow of water or by wiping it over my leg then is that sufficient?

Your ghusl is tarteebi Which means wash in order
First head and neck.
Then step out from shower then right part from shoulder till feet from up to down. While washing right part, for precautionary reason wash bit from left too to make sure nothing left unwashed then step out from shower. Finally left part in same manner.