This is indeed a shitty situation. When gluing down engineered hardwood there's always going to be spots that need to be weighed down. Cupped/warped planks, Minor low spots, etc. The whole situation probably could have been remedied with a few sandbags, glue buckets, tool boxes...... anything with some weight.
The good news is that it can be saved by a competent floor installer. It'll take some time and finesse but can be done. If the areas that are hollow aren't that big and the low point is not that low, pulling the planks, regluing & weighting down the area should take care of it.
But as said above, document everything and don't sign ANYTHING until the job is acceptable to you and the wife. And most importantly, hold on to any money owed for that part of the job!