Is this being done from a photo print on a scanner? If so, let your scanner do the heavy lifting. Target the couple in the photo and tell your scanner to scan at at least 300 DPI for 5 x 7 or 8x10 (finished size).
If this is from a digital shot, use the crop tool set the the finished size at 300 DPI and crop the original that way. Make sure your
PS preferences (General) is set to "Bicubic Sharper") before you do this.