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Ah. This explains a bit more about your previous questions. If possible you need to make sure that your client gains ownership over his older domain.  Without access to the Registrar rights you're not going to be able to edit the nameserver and registry information to show that he owns it as well as do the necessary server side work to control the old domain. Wherever the old domain name is currently registered you'll need to contact them and inquire about the process regarding gaining complete ownership of the domain. Since your client is a lawyer he can probably be pretty persuasive in this area.

Is the established website staying active? Or is he moving all business to the new website?  If the latter, feel free to update citations as well as redirecting to the new site.  If he's keeping both websites and they're different businesses, you'll have to treat the new one as a separate entity and go through the process of developing its marketing and SEO from scratch.  Keep the old citations pointing to the original site, and work on developing new ones for the new site.  Cheers!

Nice discussion going on here, with Egol making some very good points. Personally, I am not a fan of the multi-site approach. It's the brand that needs to be built as the authority, for all of its services. And when it comes to Local, having shared NAP on more than one website can cause citation difficulties. So, again, this comes down to having a single authoritative source representing your business on the web. This tends to be the consensus of opinion on the Local SEO world - 1 site is better than 2.