Good for you for sending thank you notes and for wanting them to be targeted to each interviewer rather than formulaic.
As you point out, typos are easy to make and hard to detect. However, most administrative positions require attention to detail, and that includes proofreading carefully everything you create. (Consider, by the way, that the last sentence clause in your first paragraph is grammatically flawed.) As a result, I disagree with your comment that the "typo was not that critical". When you're trying to put your best foot forward, every mistake gets magnified.
Whether you'll get the position depends on several factors, including whether the person who received the second email noticed the misspelling, how much "pull" that person has among the three interviewer team, and whether you have other strong qualifications for the job that other interviewees don't have.
In the future, you may want to try increasing the detection rate of your proofreading with these suggestions:
- Read the letter backwards, one word at a time. When you're focusing on just one word, you're more likely to detect misspellings
- Read the letter out loud, slowly. This will help you find awkward sentence construction, bad grammar, and typos.
- Print out critical writing and read it from the paper copy (with apologies to the environment). Words on the screen just don't look the same as words on paper. You'll be amazed at the mistakes you find.
- Ask someone else to read over what you've written -- before you send it.
These aren't tools just for good administrative staff members. The best executives use these, too, so consider making them a life-long habit.
Best of luck!