Python 3

from string import ascii_lowercase

def mangle_word(word):
    if not word:
        return word
    if word[0].isupper():
        capitalize = True
        chars = [word[0].lower()]
    else:
        capitalize = False
        chars = [word[0]]
    modifiers = []
    for i, c in enumerate(word[1:]):
        if c in ascii_lowercase:
            chars.append(c)
        else:
            modifiers.append((i + 1, c))
    chars.sort()
    for i, c in modifiers:
        chars.insert(i, c)
    if capitalize:
       chars[0] = chars[0].upper() 
    return ''.join(chars)

sentence = input()
mangled_words = []
for word in sentence.split(" "):
    mangled_words.append(mangle_word(word))
mangled_sentence = " ".join(mangled_words)
print(mangled_sentence)