With kitchen counters that thick, I believe they face the counter with a layer of ply to support the stone. I wouldn't think that the sink would have problems with the thickness, the weight of the stone and the sink might make the slab crack if not supported across the vanity span. You could post this question over on the kitchen forum too.

I know nothing about its quality but I have been thinking of this for my downstairs bath in my 20s house. It is really cheap at less than 250.Not a lot of storage but it seems more appropriate for the era of the house. And far less than the one I have been coveting from kohler's memoir line https://www.qualitybath.com/american-standard-0282-retrospect-bathroom-console-table-sink-19-34-w-x-27-d-x-36-h-product-216091.htm?sku=0282.004.020&gclid=CjwKEAiAkuLDBRCRguCgvITww0YSJAAHrpf-0aoNnZmpeVhGEvnUy0LE_87lQ4VAfLbD267suP1AfRoCcoXw_wcB

Good point Zookeeper63!. At the moment we all huddle in to the master bathroom while the kids shower together, and we all have a family teeth brushing session so it feels like we need the two sinks - one parent, one kid to a sink. You point out correctly that that will not likely be the case as they grow older, or if we have guests. The vanity we are choosing would either have two big drawers, or four drawers. I assume that this would be enough storage for extra things - hair dryers, toilet rolls, toothpastes, shampoos etc. But, if we go the single sink route, it gives us room to instead also have a tall cabinet which would add even more storage. In fact, with that, we could skip getting the Godmorgon (medicine cabinet style) mirror cabinets and just use the tall cabinet for storage. Good pointers Zookeeper63. Almost feels obvious but, obviously not! :) Thank you.

As long as it's in the lowest part it will function properly.