Always. If it is an owner occupied, seller always know who and when is coming.

No.  If the contract doesn't call for it - the Seller shouldn't "expect" it...

I think the buyers' agent was the one that knew how many folks would be there.  Just out of courtesy I would have let that be known, and mentioned that it is also going to be more conveneint for the sellers, as you mentioned, Jeffrey Jones.

I have had more issues with showings where the buyers want to bring through moms, dads, uncle Ted, et al, to see the property.  I now address that well in advance when I start working with new buyer clients.

Jeffrey,

It isn’t the norm here to let the seller, via their agent, know who will be there.

The buyers that I have worked with have not brought a contractor on the day of the inspection. They sonetimes bring their parents . 

 Good Tuesday morning Jeffrey. As long as the inspections were done within the same timeframe I don't see the reason the sellers would be all upset.

That is not the custom in this area.  You let the listing agent know the date and time, and usually the buyers and listing agent are there.

Our agreements spell out they types of inspections, testing is another matter that requires another form to be agreed to.  As far as estimates from a contractor, that is something that should have been addressed before the offer was written since their opinion will have no bearing on the contract.

As a courtesy I would have notified the sellers of everyone who is coming to their home.  All it takes is a 30 second phone call. The seller most likely would have agreed to allow the contractor to come but just wanted a say in the matter.