Misafirler gelmeden önce salonu toplamalıyız.

Gelmeden önce means before coming / before someone comes.

It is built from:

• gel- = come
• -meden = without doing / before doing in this kind of structure
• önce = before

So:

• gelmeden önce = before coming
• in this sentence: before the guests come

A very common pattern in Turkish is:

• verb stem + -madan/-meden önce = before doing ...

For example:

• çıkmadan önce = before leaving
• yemeden önce = before eating

Because gelmeden önce is not a fully conjugated finite verb form like geliyorlar or gelecekler. It is a subordinate verb form.

In this structure, Turkish usually does not add person/plural endings to the verb. The subject is understood from the noun that comes with it:

• misafirler gelmeden önce = before the guests come

So the plural idea comes from misafirler (guests), not from a plural ending on gelmeden.

The -u is the accusative ending, marking a specific direct object.

• salon = living room / lounge / hall
• salonu = the living room / the specific living room, as the thing being tidied

Since toplamak here acts on a specific room, Turkish uses the accusative:

• salonu toplamak = to tidy up the living room

If you leave off the accusative, it would sound incomplete or unnatural here.

Yes, toplamak often means to collect or to gather, but it also very commonly means to tidy up / put in order.

So depending on the object, it can mean different things:

• para toplamak = collect money
• oyuncakları toplamak = gather/put away the toys
• odayı toplamak = tidy the room
• salonu toplamak = tidy the living room

Here it clearly means tidy up.

Toplamalıyız breaks down like this:

• topla- = tidy up
• -malı / -meli = must / should / need to
• -yız = we are / we

So:

• toplamalıyız = we must tidy up / we should tidy up

The y is just a buffer letter because -malı is followed by a vowel-initial personal ending.

Because the verb already shows we, Turkish does not need a separate biz.

Not always. It can mean:

• must
• should
• need to
• sometimes a strong recommendation or obligation

The exact strength depends on context and tone.

So salonu toplamalıyız could mean:

• We must tidy the living room
• We should tidy the living room
• We need to tidy the living room

In this sentence, must/need to is a very natural reading.

This is very natural Turkish word order.

A common pattern is:

• time clause + object + main verb

So:

• Misafirler gelmeden önce = before the guests come
• salonu = the living room
• toplamalıyız = we must tidy up

Turkish often puts the main verb at the end. Also, time expressions and subordinate clauses often come near the beginning.

You could move things around for emphasis, but this version is very standard and natural.

Usually, if you want to clearly mean before, you should keep önce:

• gelmeden önce = before coming

Without önce, gelmeden often means without coming or can sound incomplete by itself.

So for learners, the safest rule is:

• verb + -madan/-meden önce = before doing
• verb + -madan/-meden by itself often = without doing

Turkish has no word like English the or a/an. So misafirler can mean:

• guests
• the guests

In this sentence, English will usually translate it as the guests, because the situation sounds specific:

• Before the guests come, we must tidy the living room.

But Turkish itself does not mark that with an article.

In Turkish, salon often means:

• living room
• lounge
• hall

In a home context, salon usually means the living room/main sitting room.

So salonu toplamalıyız most naturally means:

• we need to tidy up the living room

Yes, you can, but it is usually unnecessary.

• Toplamalıyız already means we must tidy up
• so biz is normally omitted unless you want emphasis or contrast

For example:

• Biz salonu toplamalıyız, onlar mutfağı. = We should tidy the living room, and they should do the kitchen.

In your sentence, leaving out biz is the most natural choice.