It isn't clear why K.'s uncle is called Karl when he's first introduced, then Albert later on in the novel when he meets with Huld. It may have something to do with the fact that Kafka's novel was unfinished and Kafka didn't have the chance to regularize the names.
K.'s uncle pops up to reprimand K. for neglecting his trial, and introduces K. to Huld. The fact that K.'s uncle is actually a man from the country (visiting K. in the city) may be significant given that the parable of the Law in Chapter 9 stars a "man from the country." This parallel may stress the uncle as a voice for the ordinary man, the everyman, and the uncle's appeal to traditional family ties seems to support this view. The fact that K. too was raised in the country by his uncle suggests that, like the man in the country in the parable, K. is in some ways an outsider in the modern, urban setting of the courts. But K.'s dismissive attitude toward his uncle suggests his rejection of the traditional values that his uncle represents as well.