Ellis had a non-finish and a third-place finish on the LCR Honda 600cc outfit, while his step-father Bryan raced the LCR 1000cc Kawasaki outfit to second place in both races.
Ellis and his passenger Charlie Richardson got away well in the first race and were running third until a coming-together with Stevens and Charlwood at the first corner on lap two forced them off the track and out of the race.
Meanwhile Bryan, with passenger Phil Hyde, got the hole shot at the start and led the field around the first lap before they were overtaken by Kershaw and Clark on lap two.
But they continued to pull clear of the pursuing pack and secured a comfortable second place in the 12-lap affair.
Starting race two the following day from the back of the grid on row eight, Ellis and Richardson had plenty of work to do to get on terms.
But Ellis got his head down and ploughed through the back markers to take up eighth at the end of the first lap.
They made up another two places on lap two and were up to fourth on lap four, following Horspole and Connell for two laps before passing them at Mansfield to take up third place.
They were too far adrift of the leading outfits and had to be content with third at the flag.
They were the first 600 Cup competitors over the finish line and claimed 25 points to bring their total to 349 for a comfortable 53-point lead over Stevens and Charlwood with two rounds left.
Bryan and Hyde started race two from row four and started well to move into fourth on the opening lap.
One lap later they were third and then passed Horspole and Connell at Mansfield on lap three to take up second place.
With the frontrunners too far ahead, Bryan and Hyde stayed second to the chequered flag for another 20 points, taking their total to 254 to stay third in the championship.
The next round is at the Dutch circuit of Assen from September 28 to 30 when both teams will be seeking top results to boost their points tally ahead of the final round at Brands Hatch.