Politeness / political correctness and gender polarity of “plural” suffix -等(ら) for 彼 and 彼女 etc

Question

The definitions on ejje.weblio:

• 彼ら
• 彼女ら

What I would like to know is:

1. 彼ら is definitely gender neutral and 彼女ら can only have females in the group, right?
2. As explained in Why is “学生” made “plural” in this newspaper article?, adding -ら allows for a more precise statement. But I wonder, do they sound impolite and rough and would not be used in newspapers?
3. Is 彼ら rarely used in speaking? And never in writing?
4. Is 彼女ら just never used?
5. Is あいつら not uncommon, but used in extremely informal conversations?
6. You cannot substitute たち for ら and say 彼たち, 彼女たち, or あいつたち, right?

Answer 1

彼ら is definitely gender neutral and 彼女ら can only have females in the group, right?

If you think using he in English when the gender is unknown is politically incorrect, then you would still want to worry about 彼ら a bit, too. You don't have to be too strict, but avoiding gender-neutral 彼ら when possible is a good habit.

And I think the singular 彼 strongly indicates the male gender, perhaps even more strongly than English he.

Adding -ら allows for a more precise statement. But I wonder, do they sound impolite and rough and would not be used in newspapers?

彼ら and 彼女ら are used both in formal and casual situations. There's nothing impolite.

Is 彼ら rarely used in speaking? And never in writing?
Is 彼女ら just never used?

They are used both in casual speaking and writing, but not as frequently as he/she/they is used in English. Repeating the original noun (e.g. 学生たち, その人たち, 山田さんたち), or simply omitting such pronouns, is the preferred way in Japanese.

Is あいつら not uncommon, but used in extremely informal conversations?

あいつら (as well as こいつら, そいつら) is more than just informal; it's rough, and frequently (not always) used in derogatory sentences. I would never use あいつ(ら) unless I'm really upset.

You cannot substitute たち for ら and say 彼たち, 彼女たち, or あいつたち, right?

彼ら, 彼女ら and 彼女たち are all commonly used, but 彼たち is extremely uncommon for some reason. I don't know why. But you can check this article.

Answer 2

彼ら is definitely gender neutral and 彼女ら can only have females in the group, right?

Japanese plurals are (or at least can be) associative. 彼ら means "he and the ones I/we associate with him", just like 田中たち doesn't necessarily designate a group where everybody is called Tanaka, but means "Tanaka and the ones associated with him/her". So 彼ら would usually have a male representative, and 彼女ら would have a female representative. Not everybody would have to be female. See previous question here: What rules should be followed when saying "we"?

You cannot substitute たち for ら and say 彼たち, 彼女たち, or あいつたち, right?

たち and ら are both quite productive (i.e. you can attach them to almost all kinds of animate nouns/pronouns), but ら has an affectionate/derogatory nuance:

広辞苑･･･ら[等]
①体言の下について複数を表す。
②人を表す名詞や代名詞に付いて、親愛・謙譲・蔑視の気持ちを表す。

彼ら is an exception, since as @naruto says, 彼たち is uncommon. Also, あいつたち is, I guess, possible, but sounds strange, since あいつ already has affection/derogation built in and therefore goes better with ら.