When Joey was a toddler - old enough to scale fences and leap from playground equipment but not old enough to talk - Peter acted as translator between his parents and his younger brother. After Joey learned to talk, he and Peter would not again be on speaking terms for a decade until their friendship was reforged in the crucible of morning practices and distance sets.
Though Joey technically followed Peter to Kenyon College, his achievements in and out of the pool shortly change things from "Peter's brother Joey" to "Joey's brother Peter." After graduation, Joey joined Peter in DC and was a regular fixture on his couch (both socially and residentially) and they even worked together for a time as opposition researchers. There is no one to whom Peter would rather turn for sartorial advice or a quick loan.
Joey currently lives in Oakland, California where he plays god with the state's energy supply.