Is it a concern or even possible conflict of interest for a licenced Investment Advisor Representative to advance themselves to also be the Executor

Your intuition is correct: it is neither normal nor common for an investment advisor to seek to become the Executor or a trustee under a client's estate plan, unless that client is also a family member of the investment advisor. Your wife's parents are best advised to seek a different investment advisor. They may also want to seek a different attorney, if their estate planning attorney isn't telling them that this is a red flag. In my experience, most investment advisors are not even ALLOWED by their broker-dealers to serve in fiduciary roles for clients. Even attorneys, who are allowed to do so under the state Bar's ethics rules, can only do so under very limited circumstances, and cannot suggest to the client that the client choose the attorney (the client has to come up with that request on his or her own, and then the attorney must fully explain potential conflicts of interest that the attorney's service will create, along with the other options for someone who could serve in that role instead of the attorney. Best wishes to you, your wife, and her parents. I hope they will move away from that advisor.