beranda no kagi ga sukosi hen datta node, kanrigaisya ni kite moraimasita.

It can be either. In Japanese, 鍵 is often used for both key and lock, depending on context.

In this sentence, the lock is probably the more natural reading:
ベランダの鍵が少し変だった = the balcony lock was a little strange / not working quite right.

If the actual metal key itself was bent or odd, key could also make sense, but many learners should be aware that Japanese does not always separate key and lock as clearly as English does.

The particle の links two nouns.

• ベランダ = balcony / veranda
• 鍵 = key / lock

So:

• ベランダの鍵 = the balcony’s key/lock
• more natural English: the balcony lock or the key to the balcony door

This is a very common pattern in Japanese:

• 部屋のドア = the room’s door / the room door
• 車の鍵 = the car key

Here, が marks the thing that had the condition.

• 鍵が少し変だった = the lock was a little strange

This is a straightforward description of what was wrong.

If you used は, it would sound more like you are making 鍵 the topic, possibly with contrast:

• ベランダの鍵は少し変でした = As for the balcony lock, it was a little strange

That is also possible, but が is very natural when introducing the problem itself.

Because 変 is a na-adjective.

With na-adjectives, the plain past form uses だった:

• 変だ = is strange
• 変だった = was strange

So:

• 鍵が変だった = the lock was strange

This is different from i-adjectives, which change differently:

• 高い → 高かった
• 変 → 変だった

少し means a little or slightly.

So 少し変だった means:

• a little strange
• a bit odd
• not quite right

In real-life Japanese, this often softens the statement. It may not mean only a tiny problem in a strict mathematical sense. It can simply mean the speaker is describing the issue in a mild, non-dramatic way.

ので gives the reason: because / since.

So:

• 鍵が少し変だったので = because the lock was a little strange

Compared with から, ので usually sounds:

• a little softer
• more explanatory
• a bit more objective or polite

So this sentence has a natural explaining the situation feel:

• The balcony lock seemed a little off, so I had the management company come over.

This is the pattern:

• て-form + もらう

It means to receive the favor/benefit of someone doing something.

So:

• 来て = come
• もらいました = received the favor (polite past)

Together:

• 来てもらいました = I had them come / I got them to come / they came for me at my request

It does not just mean they came. It implies that the speaker arranged it, requested it, or benefited from that action.

With てもらう, the person or group who does the action is often marked with に.

So:

• 管理会社に来てもらいました
• literally: I received the favor of the management company coming

In natural English:

• I had the management company come over
• I got the management company to come
• I asked the management company to come by

So に marks who performed the action for the speaker.

Literally, the sentence says the management company came, but in real usage it means someone from the management company, such as:

• a staff member
• a building manager
• a repair person they sent

Japanese often uses the organization name even when only one representative actually comes.

Here it usually feels like come over or come by, because the person is coming to the speaker’s place.

Since the sentence is about a balcony lock and a management company, the implied location is probably the speaker’s apartment or home.

So in natural English, come over is often the best match.

Yes, that is strongly implied, but it is not stated directly.

The sentence specifically says the speaker had the management company come. That means the speaker must have arranged it somehow, probably by calling or messaging them, but the method of contact is not mentioned.

So the sentence is about the result:

• the lock seemed odd
• therefore the management company came over

Not about the exact way the speaker reached them.