Hi Marcus,
Really a very complex case.
Possum is tough! Also you are right, Penguin is playing also.
I think that Google see Event R us as the main website and Fantastic Events as the attempt to deceive, mostly due to age gives authority.
From SEO strictly speaking, nothing else to do. Even more, the owner of the Fantastic Events should not be the owner of the new domain, if he decides to move.
Said that.
Brainstorming, before advice to move and start over. I would try some out of the box thinking/options.
1.- The fist step should be: address might be changed a little, by going to the city council and/or the post office and asking for a differentiation like Beaumont Farm - B.
Sending the new NAP, with the B to all aggregators asap. After that, setting up 2 GPS tracking devices as far as possible, with the B for Fantastic Events and using an online service, known due to Google follows it as related company or business partner.
2.- Sending to Google the official registration of the business and the tax payments, as well (one of my clients was required to do so for register a second address in another country).
It could be used to prove that both business, though they are family related, do not belong to the same person. As far as I know, many automatic algorithms can be lifted manually by Google.
3.- By a very intensive social media campaign from Fantastic Events which includes the name of the proprietor of the company.
As we all know, though Social Media will not help the website itself, Google reads and understands Social Media signals completely. In that case, using companies no related to Google, like Facebook - as far as I know - Twitter and LinkedIn. Perhaps some paid ads also. Google does not like when clients pay somewhere else. It seems they have algorithms to call back and offers help and support...
4.- Also, a very intensive campaign using Google tools, ie. Google+ and reviews which includes strong signals to differentiate Fantastic Events from Event R us.
5.- If data from Uber, Netflix and Tinder Insights might sink a person, what about getting a different cable provider for the Fantastic Events. Using Uber with the new B & the GPS in place.
Due to it seems that all the algorithms are rolling continuously, if some of the measures have results, it will be within a month, after the B in place. As far as I understand, none of the above moves are expensive.
In the event that everything fails, your client will have to move, and sue Google - yes, it can be done, perhaps with the help of an Org or a reputed Law School - so keeping all the records is very advisable. As well as an aggressive campaign by twitter and exposing the issue to the Media, if your client is willing to fight back, of course.
Wish you success.
P.S. On the contrary, if your client changed his address, tell him do not log in Google, Uber, Netflix, etc., in or in the vicinity of his father business.
Those would be very contradictory signals.
Modified November 1st.