Brothers have served in the House of Representatives at the same time. Frederick Muhlenberg of Pennsylvania and John Peter Gabriel Muhlenberg of Pennsylvania, served in the 1st and 3rd Congress.
Also, Israel Washburn Jr. of Maine, Elihu Brown Washburne (apparently he preferred to have an ‘e’ at the end of his name) of Illinois and Cadwallader Colden Washburn of Wisconsin served from the 46th to 48th Congresses simultaneously.