Speaking as someone who believes the design work belongs to the client (who else is gonna use it?) I can’t understand this concept of expecting royalties for graphic design.
You don’t say what kind of business this is that your brother runs, or what kind of services he needs.
I could understand royalties if you were, for instance, designing illustrations for t-shirts. But not for designing the packaging those t-shirts are wrapped in when sold.
Requiring royalties for illustration usage is an entirely different concept from the way graphic design is billed out. And even then, the rights are usually offered per a set number of units sold, not a per each. The business buying the art might pay up front for, let’s say, up to 10,000 impressions of an image for a set fee. It’s up to them to then sell the 10,000 pieces, while you still have the money they paid for the imagery. You are basically selling a stock image. This doesn’t apply to specifically created graphic design.
Like Mojo said, it sorta depends on what you are calling a “basic” salary. If that salary more than covers your hourly rate and maybe even comes with some benefits like unemployment insurance and health/dental, and if it is the basic graphic design job that designs the marketing collateral to bring in business, it may be worth your while. However, depending on what country you are in, any work created while employed by another becomes the property of the company you work for pretty much automatically, so be aware, if this is an illustration job where the art sells product on a piece basis. There are also contracts drawn up as Work For Hire where anything you produce is owned by the person who contracts you (which is how logo creations works.) Even if you work on a contract basis, the work you create is pretty much geared for one specific client’s needs, which is why I don’t understand the claims of “copyright” some designers think they are entitled to. You can’t copyright a design layout, you can’t claim copyright to any supplied images or body copy (if you took the images, you can charge a royalty fee, just like a stock company but put it in your contract, and if you write the copy, there is a fee involved there too, but where else are you gonna use that copy?) There isn’t a whole lot about a designed piece that would be copyrightable. Logos always become the property of those that commission them.
As a designer, your art is a commodity to be sold. Nothing more.
Never make allowances for “family.” Always use your standard contract.
You are in business to earn a living. You might give someone the “friends and family discount” but don’t undersell yourself. Uncontracted dealings with families and friends can lead to some spectacular misunderstandings. It’s gotta be just another day at the office.