CAROLYN WYETH, 84, a member of one of America's most famous artistic families, died Tuesday in Chadds Ford, Pa. A contemporary artist, she was the sister of Andrew Wyeth, the internationally famous painter, and the daughter of the late illustrator N. C. Wyeth. Working in oil, she was noted for her landscapes of the rural Chadds Ford area and of coastal Maine. She sat for her brother for a number of portraits, including The Critic, painted in 1990. Her works hang at the Delaware Art Museum and in many public and private collections. Besides Andrew, survivors include two sisters, painter Henriette Wyeth Hurd and composer Ann Wyeth McCoy.