If the individual spindles are properly secured to both the handrail and the treads, and the handrail ends are properly secure to the existing newels, you shouldn't need the extra newels. If you do indeed need the extra newels, though, you'll need to not only secure the new newels to the treads but also have secure attachment of the handrail segments to the newels.

Thanks... Unfortunatly the current handrail and spindles are loose. Plus given the overall length of the staircase (17 steps) with only the handrail, I just don't feel its secure enough (has play in it). For the rail to the newel was thinking of using the zipbolt rail to newel connection. thanks. So right now looking for feedback on attaching the newel to the stair tread (fyi.. The trea is 1 3/4" thick. thanks

For maximum strength, you'll want to have the newels extend through the treads and attach to the stringers.

Agreed that best approach is to extend newel through tread. It will be rock solid.

That run of rail seems long enough to be out of code; check please.

Here you go.

That's not going to work going into a 1 3/4 tread.

Though I hate these brackets, they work.

Never, ever seen newel posts in the middle of a straight run of stairs. That will be a hand bruiser.

Interesting, never seen treads overhang like that.

Handrails need to be continuous, so intermediate newell posts would be against code, or you can install a handrail on the wall side.

Too long a run with a lack of support is out of code. The guardrail has to be able to withstand 200 lbs. without failure.