Wij lichten de catering in voordat Sofie opduikt.

Both wij and we mean we.

• we is the unstressed, much more common form in everyday Dutch.
• wij is the stressed form, used for emphasis, contrast, or slightly more formal style.

So:

• We lichten de catering in = the most natural everyday version
• Wij lichten de catering in = we inform the catering staff, possibly with emphasis on we

In many sentences, either one is possible.

Lichten ... in is the separable verb inlichten, which means:

• to inform
• to brief
• to notify

So Wij lichten de catering in means We inform the catering staff.

This is not related to the literal meaning of lichten as to lift or to lighten. You need to learn inlichten as one complete verb with its own meaning.

Because inlichten is a separable verb.

In a main clause, separable verbs split:

• Wij lichten de catering in.

Here:

• lichten = the conjugated part
• in = the separated prefix, which goes toward the end of the clause

This is very common in Dutch:

• opbellen → Ik bel je op.
• aankomen → Zij komt morgen aan.
• inlichten → Wij lichten de catering in.

Because opduikt is inside a subordinate clause introduced by voordat.

In subordinate clauses, separable verbs usually do not split. The whole verb stays together at the end:

• main clause: Sofie duikt op.
• subordinate clause: voordat Sofie opduikt

So:

• Wij lichten de catering in → main clause, separable verb split
• voordat Sofie opduikt → subordinate clause, separable verb stays together

This is a very important Dutch pattern.

Because voordat means before, and it introduces a subordinate clause.

In Dutch subordinate clauses, the verb typically goes to the end. That is why you get:

• voordat Sofie opduikt

rather than an English-like order.

Compare:

• main clause: Sofie duikt op.
• subordinate clause: voordat Sofie opduikt

So the sentence structure is:

• Wij lichten de catering in = main clause
• voordat Sofie opduikt = subordinate clause

Here opduiken means something like:

• to show up
• to appear
• to turn up

So voordat Sofie opduikt means before Sofie shows up / appears.

Depending on context, opduiken can suggest appearing somewhat suddenly or unexpectedly.

In context, de catering usually refers not just to the catering as a service, but to the catering team, the caterer, or the catering staff.

So:

• Wij lichten de catering in
  means
  We inform the catering staff / the caterer

Dutch often uses a service or organization name to refer to the people responsible for it.

Yes, it is in the present tense, but Dutch often uses the present tense for the near future, just like English sometimes does.

So:

• Wij lichten de catering in voordat Sofie opduikt.

can mean:

• We inform the catering staff before Sofie shows up
• We’ll inform the catering staff before Sofie shows up

Dutch does not always need a separate future marker like zullen.

Yes. You can also say:

• Voordat Sofie opduikt, lichten wij de catering in.

That means the same thing.

Notice what happens in the main clause after the subordinate clause comes first:

• lichten wij instead of wij lichten

This is because Dutch main clauses follow the verb-second rule. If the voordat clause takes the first position, the verb comes immediately after it.

The verb inlichten normally takes a direct object for the person or group being informed.

So Dutch says:

• iemand inlichten = to inform someone

That is why you get:

• Wij lichten de catering in.

and not normally Wij lichten aan de catering in.

Examples:

• Ik licht de directeur in. = I inform the director.
• Ze lichten ons in. = They inform us.

Yes, it is grammatical and natural.

A slightly more everyday version would probably be:

• We lichten de catering in voordat Sofie opduikt.

because we is more common than wij in ordinary speech unless you want emphasis.

So the sentence is fine as it is, but we may sound a little more conversational.