4th/replacement LOR questions.

[Meghanlodon]

So my original third letter writer has never gotten back to me after I first asked (went on sabbatical, I sent him what I had but no acknowledgement it was received.)  I asked a fourth person to provide a backup letter (or replacement,) and I had a couple questions regarding this situation:

When I send update emails, do I include the original third letter writer? I mention the letter writers in my statement (what I learned from them and how it relates to my potential research,) should I edit the original writer out before I apply to programs?