Fred knew it was difficult for anyone who wasn't a Weasley to keep track of them all. In truth, it was probably difficult if you were a Weasley at times. He didn't fault anyone for that and had gotten as used to people being uncertain about which Weasley was which years ago.
Fred smiled at the compliment — he totally took it as a compliment, of course. "Well, I do try," he told Higgs. "You're alright, too, Higgs. Definitely more interesting than standing here silent the whole queue," he said. Which made him think that maybe they should chat again somewhere not so random as a post office. "We should have drinks sometime," he commented. "It'd probably do you some good. I'll even buy you the first one."