Is it inhumane to call aliens men?

A fairly common source of lexical awkwardness in scifi and fantasy is the inhumane disregard of the fact that appealing to the humanity of a non-human or simply referring to them as man is probably rather offensive.
The worst offender is probably Star Trek: Cpt Picard loved appealing to someone's humanity. The show may have produced the quote that "the federation is no more than a Homo sapiens only club", but that is no justification for sloppy language.

Firstly, what is a better word for humanity?
Humanity has four meanings:

• the collective term for humans. Synonym: mankind.
• the quality of being human. No synonym as manly means masculine.
• the abstract noun of humane (not human). Synonyms: compassion, benevolence, kindness, magnanimity.
• the arts. Also from humane.

So basically the use of the words humane, inhumane and humanity are signs of sloppy writing as compassionate, cruel and compassion would do nicely.

Secondly, what is the collective term for certain races?

There are very few examples to work off and they are not consistent.
The suffix -kind is an Old English suffix present in mankind, it is better than the Latin suffix -ity as the latter is added to adjectives to also make abstract nouns (mens, mentis (mind) noun > mental adj. > mentality abs. noun). Hence the fact why humanity means both mankind and mannishness.

Technically, mankind is a one off combination in the dictionary. Another one that was lost is Angelcynn (Anglekin). Note that it is from the noun angel (Angle), not the adjective ænglisc (English, pertaining to the Angles) similarly to mankind and not mannishkind. Somewhere along the way the words elvenkind and dwarvenkind appeared, which are both of which are from the adjective.

Parenthetically, the adjectives of non-human races are absent in many cases, so adding -ish or -ic makes the word sound unusual in the first place —as -ish isn't constructive, while -ic sounds odd on words that don't stem from Latin/Greek.
Tolkien made a curious distinction between elven/dwarven and elvish/dwarvish in that the former adjectives mean "pertaining to x", while the latter mean "made by x". Orcish doesn't have a similar division (Orcadian is someone from Orkney). Orckind has more google hits than orcishkind and follows the pattern of mankind. Similarly, goblinkind and trollkind are less convoluted than having to make up an adjective: goblin is from Old French (gobelinic?), while troll is a Swedish recent loanword (trollisk?).
What about Latinate words? Gnomes > gnomic and dragons > draconic. Gnomekind vs. gnomickind?
The former sounds better again due to the lack of the c'k cluster. The alternative, following humanity is gnomicity and draconity, but they do sound like the quality of being a gnome/dragon.
On the flipside, when there is a consonant clash like elfkind or dwarfkind the adjective sounds better Similarly Scottishkind sounds better than Scottkind and felinekind sounds better than catkind —although felinekind and felininty might have some ablaut change kicking in (/fi:lɑjn/ > /fəlɪnəti:/).
So in conclusion, there does not seem to be a strict rule to adding -kind.

Secondly, is a man human only? And what about the suffix -man?
Well, yes and no. The word man generally refers to male humans only, but derived terms generally don't.
The word man itself is weird in that it used to mean both genders, with woman and hipman as the gender specific ones. That is why the word mankind is the collective noun for all humans.
Irrespective of etymology, nowadays there are many case where the -man suffix is replaced with person, when a woman has that task, e.g. chairperson. However it sounds so weird that probably taking the etymological standpoint for the suffix -man is the best bet. Vulcan crewperson sounds like one is trying hard to be polically correct, while Vulcan crewman sounds fine.
In Star Trek The Original Series Spock calls himself, and is called, a man on many occasions… but then again he is a Vulcan who speaks Vulcan and is from Vulcan, a planet orbiting the star Vulcan (40 Eridani).
In Star wars Legacy John Ostrander adds colour to the dialogue by adding Huttese or Mandalorian swearwords or terms of endearment. One cool thing is the use of the word sentient instead of man or person and it works really well. By extension, sentiency would be the collective term for all sentients.

In conclusion, sentient and compassion work really well to replace the words man and humanity, while the suffix kind does not have any clear rules.