def find_close_packages(packages):
    """
    Given a list of packages, find the two packages who have all but one letter in common in a position
    :param packages: list of packages
    :return: the common letters

    >>> find_close_packages(['abcde', 'fghij', 'klmno', 'pqrst', 'fguij', 'axcye', 'wvxyz'])
    'fgij'
    """

    for p1, p2 in [(packages[i], packages[j]) for i in range(len(packages)) for j in range(i, len(packages))]:
        common_letters = [p[0] for p in zip(p1, p2) if p[0] == p[1]]
        if len(common_letters) == len(p1) - 1:
            return ''.join(common_letters)

    return None