group shapes into new shape/object, not group, then edit

[ggsmit]

hi folks, this must be something elementary but my 'watsonian' brain just cant figure it out.
i have three rectangles on the same layer. the broadest one at the back, second rectangle ['band'] forward and the narrowest one up front, like a country's flag.
my objective is to shape/mould them with the shape tool AS ONE GROUP in order for the colour bands to behave like a cloth, say a flag moving in the wind.... would that be possible?
i've tried grouping them but they stay a 'group' and obviously they will have to start behaving like a single object...
i attach a jpg of what i mean
at wit's end, calling all pockets
tx in anticipation
gabriel