You don't need boating advice, you need leadership advice and inreased confidence in your own abilities.
A king is a king, except in his own home and with his own family.
You need to go to the source. If other people are telling your wife what to do, you need to go directly to the good samaritans and set things straight. Tell them politely, but directly that while you appreciate their willingness to please that you need them to stop giving your wife directions counter to your own. Often, the friendly advice is coming to fill a vacuum. Meaning that if they understood your plan prior to putting it in execution, that they would not being giving her conflicting advice. They may well disagree with your approach. It's up to you whether you want to consider the help they are offering or give them a polite "thank you, but maybe next time". Do it firmly and politely. The polite part is not optional. If you blow up, you give up your control of the situation. If you do accept advice, don't also give up control. Repeat the advice, but as your own orders and be specific about what, who and when. Give separate instructions for each player. You will retain your control and show that you understood the advice. Get agreement from the players individually before starting execution. The moment somebody starts doing something undirected, NICELY call them BY NAME. You must do it immediately and confidently and use a tone to get their attention NOW. Be nice. Stand where you can be heard and project quick and concise orders without sounding rushed. Rarely do you need to be immediately at the controls when throwing lines and a walk from the side of the boat to your shifter controls should not be too far. If you have canvas getting in the way or other barriers that makes this impossible, then invest in a solution to correct the problem. You can't run a boat without access to see and bark quick orders to bystanders. That's a fatal design flaw if you have one. If you have only a two second walk to your vantage point and that is not sufficient, then brush up on your skills.
Square your shoulders, smile but give no quarter. Somewhere your body language is betraying you. If you don't want any assistance, be sure to call all potential parties together ahead of time and politely let them know. If you want some assistance, tell them exactly what you want them to do. Confusion does not happen when discussed ahead of time. If you have confidence you will not offend, but if you are uncertain deep down you will only come across as a defensive dog biter. A defensive dog biter aggressively and prematurely bites because he is scared, not because he is angry.
You may also want to beef up on your practice and gain the confidence that fills the vacuum that currently exists. You can't BS your wife and there is a reason why she currently lacks confidence in your abilities. She's wrong to try to let someone else be captain, but its not her fault that the situation exists in the first place. The worst thing you could try to do about it though is to fight your wife from shaky ground. That's the best way to bring out the worst in ourselves.
Hope you can deal with the direct tone. Sugar coating is not one of my strong suits.
P.S. If you ever have a plan, but the plan changes as it is typical to do when dealing with something you can't control such as mother nature, be ready to bark orders immediately in rapid fire way. Dream up a list of things that might need to be done and be ready with orders, any orders. If there is one thing that will cause your crew to find new and creative ways to mess you up, its when you go silent while trying to figure out your next move. That's the exact moment when you need to start barking orders to your crew to get them busy. A busy crew does not have time to come up with their own plans of action and a boat can only have one captain, even if its a bad one. It's best if the orders you give can have some benefit, but busy you must make them. Here's a gem "I need you to stand on the Port Stern and start calling out distances every 5 seconds. Don't throw any line until I tell you". The distances might not serve any real purpose at all, but they won't hurt either and women are naturally genetically inclined to ignore the best advice in the world when they themselves are in a position to both talk and be heard (or think so).
