Perhaps with the presence of the newborn, your toodler gets excited and overwhelm. You can try to separate NB and toodler while the NB get some sleep. But it is also good for NB so that they are used to all the quiet and noises around. Unless your toodler dont scream near to NB then there shouldn't be any problem. You can also explain nicely to your toodler and make them understand to give private quiet time for your NB. It is hard but it will take time.