keiyakusyo ni syomeisuru mae ni, haha ni mite moraimasita.

With 署名する, the thing you sign is commonly marked with に:

• 契約書に署名する = sign the contract
• 名簿に署名する = sign the list

The idea is close to put your signature on something.
In English, we usually say sign the contract, so を may feel more natural to an English speaker, but に is very common with 署名する in Japanese.

This is a very common pattern:

• dictionary form of verb + 前に

It means before doing ...

So:

• 署名する前に = before signing
• 食べる前に = before eating
• 寝る前に = before going to bed

Here, 前 is a noun meaning before or in front, and に marks the time point.

Because with 前に, Japanese normally uses the dictionary form of the verb.

• 署名する前に = before signing
• 行く前に = before going
• 読む前に = before reading

The logic is that the action has not happened yet at that point.
In this sentence, the mother checked the contract first, and the signing happened afterward.

It comes from:

• 見る = to look at, see
• 見て = te-form of 見る
• もらう = to receive

The pattern Vて もらう means to receive the favor of someone doing V for you.

So 母に見てもらいました literally means something like:

• I received my mother’s looking at it for me

In natural English, that becomes:

• I had my mother look at it
• I got my mother to check it
• My mother looked it over for me

In the pattern Vてもらう, the person who does the action is marked with に.

Examples:

• 友だちに教えてもらった = I had a friend teach me
• 先生に見てもらった = I had the teacher look at it
• 母に見てもらいました = I had my mother look at it

So here, 母に means by my mother / from my mother as a favor.

The object is omitted because it is obvious from context: the contract.

Japanese often leaves out words that are already understood. A fuller version could be:

• 契約書を母に見てもらいました。

But since 契約書 has already been mentioned, it is natural to omit it in the second part.

Not really. In this context, 見る means something more like:

• look over
• check
• review
• examine

So the sentence is not saying the mother merely glanced at the contract. It strongly suggests that she checked it before the speaker signed it.

When talking about your own mother to someone else, Japanese normally uses 母.

• 母 = my mother, used when referring to your own mother
• お母さん = mom / mother, often used when addressing her directly or referring to someone else’s mother politely

So in this sentence, 母 is the standard and natural choice.

It is omitted.

Japanese very often leaves out the subject when it is clear from context. In this sentence, the person who had the mother check the contract is understood to be the speaker, so English naturally supplies I.

A more explicit version could include 私は, but it is usually unnecessary:

• 私は契約書に署名する前に、母に見てもらいました。

They are quite different:

• 母に見せました = I showed it to my mother
• 母に見てもらいました = I had my mother look at it for me

見せました only tells us that the speaker showed it to her.
見てもらいました adds the idea that the mother looked at it as a favor, probably to check or review it.

Yes, but the nuance changes.

• 母に見てもらいました focuses on the speaker receiving help
• 母が見てくれました focuses on the mother kindly doing the action

Both can be translated similarly, but てもらう emphasizes I had someone do this for me, while くれる emphasizes someone did this for me from the giver’s side.