Can the grill, fridge and the burners be attached to each other

Our grills do not lock together, however, you can set them right next to each other and lock the castors so that they do not move.

not unless you want to drill holes in the aluminum sides and bolt them together. If you don't plan on moving it, I don't see why not. The counters but up to one another, which I think prevents the sides from butting up next to one another flush, so you might need some sort of long carriage bolts, nuts and washers to compensate for the gaps.