That sounds about right. It took about 8 months from start to finish to get my husband a green card to move to the US back in 2010. It's a lot of paperwork and processing and each step takes a few months. My husband and I were super on top of things too. The minute we got approval for one step, we sent in the paperwork for the next step. I can't remember the exact specifics, but my husband did travel to the US while the green card was being processed, so I think that the Husband could start the process here in the UK. Help move his wife and child over, stay on a tourist visa for as long as he is allowed and then come back to the UK to finalize the visa.
But if the wife wants to start the job right away...yes, there will probably be some time they end up spending apart due to the lengthy process of getting a green card. And since she is the US citizen, the employer isn't being inept, but probably not doing anything because they don't have to. She has the right to work in the US. He has the right to a green card based on marriage and for a green card based on marriage, the employer wouldn't really be involved in the application.