chúfēi dàjiā tóngyì, fǒuzé búyào qiēgē.

This is a very common pattern in Mandarin:

• 除非 A，否则 B
• unless A, otherwise B
• more naturally in English: unless A, don't / won't B

In your sentence:

• 除非大家同意 = unless everyone agrees
• 否则不要切歌 = otherwise, don’t change/skip the song

So the whole structure means:

• Unless everyone agrees, don’t skip the song.

A good way to remember it is:

• 除非 introduces the exception / condition
• 否则 introduces what happens if that condition is not met

No, 否则 is common but not always required.

You can say:

• 除非大家同意，否则不要切歌。
• 除非大家同意，不要切歌。

Both are grammatical.

Adding 否则 makes the logic more explicit and often sounds a bit more complete or emphatic, especially in written or careful spoken Chinese.

So:

• with 否则 = clearer unless..., otherwise...
• without 否则 = still natural, slightly more direct

Usually yes, but it often feels very close to only if in logic.

For example:

• 除非大家同意，不要切歌。

This means:

• Don’t skip the song unless everyone agrees.
• In other words: Only skip the song if everyone agrees.

So 除非 often creates a strong condition: the action should not happen except in that one case.

Both are possible.

• 大家同意 = everyone agrees
• 大家都同意 = everyone all agrees / everyone agrees

The version with 都 sounds a little more explicitly like all. In many cases, 大家 by itself already gives that meaning, so 都 can be omitted.

Compare:

• 除非大家同意，否则不要切歌。
• 除非大家都同意，否则不要切歌。

Both are natural. The second one is slightly more emphatic.

大家 literally looks like big + family/home, but as a word it means:

• everyone
• all the people here / all of us / everybody

In this sentence, it refers to the relevant group of people, such as:

• everyone in the room
• everyone in the car
• everyone at the party
• everyone listening to the music

It does not mean each person separately in a technical way; it means the group as a whole.

In Mandarin, the object can be omitted when it is obvious from context.

Here, 同意 literally means to agree, and the listener understands the unstated idea:

• agree to changing/skipping the song
• agree that the song can be changed

So 大家同意 really means something like:

• everyone agrees (to it)
• everyone agrees with that

Chinese often leaves this kind of object unstated if it is clear from the situation.

You could make it more explicit, for example:

• 除非大家同意换歌，否则不要切歌。 = Unless everyone agrees to change the song, don’t skip it.

But the shorter version is very natural.

切歌 is a casual, modern expression. It literally means cut song, but in real usage it means:

• to change the song
• to skip to another song
• to switch tracks

This is common in contexts like:

• music apps
• karaoke
• playlists
• someone controlling the speaker or phone

It is fairly colloquial. Depending on context, it may suggest either:

• stopping the current song and playing another one
• skipping to the next song

It is mostly informal / conversational.

You are likely to hear it in everyday speech, especially among younger speakers or in situations involving phones, streaming, karaoke, or parties.

In more formal or neutral wording, people might say things like:

• 换歌 = change the song
• 切换歌曲 = switch songs/tracks

But 切歌 is very natural in casual speech.

Both can be used to give a negative command:

• 不要切歌
• 别切歌

Both mean:

• don’t skip/change the song

The difference is mainly in tone and style:

• 别 is often shorter and more conversational
• 不要 can sound a little fuller, sometimes slightly more careful or firm

In this sentence, 不要 fits well because the whole sentence has a clear rule-like structure:

• Unless everyone agrees, do not change the song.

If you used 别, it would still be natural:

• 除非大家同意，否则别切歌。

This is because of Mandarin tone sandhi.

Normally:

• 不 is fourth tone: bù

But when 不 comes before another fourth-tone syllable, it changes to second tone:

• 要 is fourth tone: yào
• so 不要 is pronounced búyào

This is a pronunciation change, not a spelling change.

Other examples:

• 不是 → búshì
• 不对 → búduì

Yes, Chinese allows some flexibility, though some versions sound more natural than others.

Original:

• 除非大家同意，否则不要切歌。

You could also say:

• 不要切歌，除非大家同意。

That version is also very natural and may feel closer to English word order:

• Don’t skip the song unless everyone agrees.

The original version is a bit more structured and formal-seeming because it uses the full 除非...否则... pattern.

Usually 大家 means everyone involved in the situation, and it often includes the speaker if the speaker is part of the group.

For example, at a party:

• 除非大家同意，否则不要切歌。
• The speaker probably means: don’t change the song unless all of us / all the people here agree

But context matters. Sometimes it can mean everyone else present if the speaker is acting as an organizer or authority.

So the exact group depends on the situation, but it generally means all the relevant people.

It can function as any of those, depending on tone and context.

With 不要, it is grammatically a negative command / instruction:

• don’t skip the song

But in real life, it could sound like:

• a house rule
• a polite request
• a firm warning
• a group norm

So the force comes from context and tone of voice. The sentence itself is neutral enough to fit several situations.

Yes. That is a very good natural translation.

Even though the Chinese uses 除非...否则..., the logic is the same:

• 除非大家同意，否则不要切歌。
• Only change/skip the song if everyone agrees.

This is often the smoothest English equivalent.

So you can understand the sentence in two equivalent ways:

• Unless everyone agrees, don’t skip the song.
• Only skip the song if everyone agrees.