This Content Originally Published by a land surveyor to Land Surveyors United Network
Almost 5 meters in position and 10 meters in height. Not good for changes that you are asking. Rent a profesional equipment from the very beginning
Like most replied here I wouldn't even attempt to collect any info with the low grade GPS. The issue being is your low accuracy device will not have relative info within itself. So the issue being is when you localize into your BM's with the survey grade GPS you will find that none of your BM's will check.
you will have to redo the survey since if you use the ones you took with the garmins the coordinates will still be inaccurate as per the required
of course, you can do it, but for example if you use a Helmert transformation the residuals will be out away of scale