Classic plumbing error not considering how the floorboards are going back when notching the joists. Since this is upstairs I do not know why you have pipe insulation, I would remove it and see if you can bring the pipes together and fit some blocks in to narrow the notches so a single T&G board will span the pipes thus you can fix either side of the pipes. If the pipe diameters will not allow that then consider what I normally do which is to lift two boards and run the pipes on the centre line of each board, it will probably mean you will have to re-install some of the pipework and making good some of the excess notching.

Richard