From pump 1 inch you should continue to branch to 3 nos 1 inch or at least 3/4 inch, not 1/2 inch until the bend going down the bathrooms you use a reducer from 1 inch or 3/4 inch into 1/2 inch. 1/2 inch with 3 outlets (not inlets) in the bathroom is ok. When you brush your teeth you are not bathing at the same time right. Also toilet will very soon full with pump in few secounds. No problem for bathing. If you use 3/4 or bigger pipe down the walls you still have to reduce the pipe to 1/2 inch at the outlets which is not advisable. Difficult to have big pipe in wall and unneccssary reducers.