Is it permissible to rinse the mouth and sniff water into the nose consecutively, but with a separation between the cupped-handfuls of water, and likewise to wipe the head and ears with separate water, and is there any sin in doing so for contravening the Sunnah?

The Sunnah for rinsing the mouth (madhmadha) and nose (istinshaq) is to use three scoops of water, rinsing the mouth and nose from each scoop. If you do this, you have followed the Sunnah. If you limit it to two times, your ablution is sufficient, even if it deviates from the more complete form. As for wiping the ears with fresh water, there is no sin in it; rather, it is considered desirable by some scholars.