Take the pyro out of the equasion because he will eventually go away.
Stabsap the engi, use his sentry as cover to cloak or disguise. Sap the second sentry and kill the second engineer.
I hope you don't mean it's that simple. The pyro is probably there to defend the sentries; he might not go away unless you wait quite awhile.
And the other engie is totally blind and can't see a sentry explode / an engie turn to ice right infront of him, yep.
Not to mention the medic could do many things. I.e use syringes or a bonesaw. Or maybe even heal the other engie / Pyro, thus making shooting at the patients very useless.
ALSO, By the looks of it, on the VERY top left corner of the picture, there is someone and a Sentry in that common sentry spot at the top of the stairs on that map, which I believe is Doublecross.