If the example is direct address (hint: his sister's name is not necessarily Anne), the commas are required.
If the sentence is not direct address, whether or not the commas are required may depend on the stylistic context, among other things. For example, The Chicago Manual of Style, 14th Edition, says this: "Unless it is restrictive (see 5.50), a word...that is in apposition to a noun is usually set off by commas...." (5.49, italics mine). Then, "If the appositive has a restrictive function, it is not set off by commas...." (5.50).
The Associated Press Stylebook (2007, p. 326) takes what at first appears to be a more didactic (more prescriptive than the comparatively more descriptive Chicago Manual) approach: "A nonessential phrase must be set off by by commas. An essential phrase must not be set off by commas."
I say 'at first' because, when you examine what's intended by "essential" and "nonessential" (pp. 87-8), you find this:
These terms are used in this book instead of restrictive phrase and
nonrestrictive phrase to convey the distinction between the two in a more easily remembered manner.
The underlying concept is the one that also applies to clauses:
An essential phrase is a word or group of words critical to the
reader's understanding of what the author had in mind.
A nonessential phrase provides more information about something.
Although the information may be helpful to the reader's comprehension,
the reader would not be misled if the information were not there.
So, in the example you give, whether the appositive phrase is essential or nonessential depends on your sense (a sense sponsored by the stylistic and semantic context) of whether or not the information is essential or nonessential.