المستندات الداعمة فيها اثبات الملكية.

Because المستندات is a non-human plural, and in Arabic, non-human plurals are very often treated grammatically as feminine singular.

So even though المستندات means documents (plural), Arabic commonly refers back to it with:

• فيها = in it / it contains not
• فيهم = in them (usually for people)

This is a very important pattern to get used to:

• الكتب فيها صور = The books have pictures in them
• العربيات فيها مشكلة = The cars have a problem

So here, فيها is completely normal.

For the same reason: المستندات is a non-human plural, and adjectives that describe non-human plurals are usually feminine singular.

So:

• المستندات الداعمة = the supporting documents

Even though this sounds strange from an English perspective, it is standard Arabic grammar.

Compare:

• كتب مفيدة = useful books
• مستندات مطلوبة = required documents
• أوراق رسمية = official papers

So الداعمة is not a mistake; it agrees the way Arabic normally handles non-human plurals.

Literally, فيها means in it or in her, depending on context. Here it means something like:

• it contains
• there is in it
• it includes

So the sentence structure is roughly:

• المستندات الداعمة = the supporting documents
• فيها = have / contain / in them there is
• إثبات الملكية = proof of ownership

A very common Egyptian pattern is:

• الملف فيه صورة = The file has a photo
• الورقة فيها توقيع = The paper has a signature

So فيه / فيها often works like has / contains in everyday Arabic.

Arabic often does not need an explicit verb in the present tense the way English does.

This is a kind of nominal sentence. Arabic can simply say:

• المستندات الداعمة فيها إثبات الملكية

Literally:

• the supporting documents — in them is proof of ownership

Natural English:

• The supporting documents contain proof of ownership
• The supporting documents include proof of ownership

So the idea of have/contain is being expressed through فيها, not through a separate verb.

Because this is an iḍāfa construction, often called a possessive/construct phrase.

Here:

• إثبات = proof
• الملكية = the ownership

Together:

• إثبات الملكية = proof of ownership

In an iḍāfa:

• the first noun usually does not take ال
• the second noun can be definite

So:

• إثبات الملكية = proof of ownership not
• الإثبات الملكية

Other examples:

• باب البيت = the door of the house
• رقم الهاتف = the phone number
• صورة البطاقة = a copy/photo of the ID card

In formal standard spelling, it should be:

• إثبات

with a hamza under the alif.

Many people omit hamzas in casual typing, so you may often see:

• اثبات

But if you are writing carefully or formally, especially in official Arabic, إثبات is the better spelling.

It feels like a formal/admin-style sentence that is very understandable in Egypt, with vocabulary that is mostly shared with Modern Standard Arabic.

Words like:

• المستندات
• الداعمة
• إثبات الملكية

are formal and common in official language.

The structure with فيها is also very natural in Egyptian usage.

So the sentence is best thought of as:

• formal Arabic used in an Egyptian context rather than very casual spoken Egyptian.

A more everyday Egyptian phrasing might be something like:

• الأوراق دي فيها إثبات ملكية or
• فيها ما يثبت الملكية

But the original sentence is perfectly understandable and suitable for paperwork or administrative contexts.

A natural Egyptian-style pronunciation would be approximately:

• el-mostanadāt ed-daʿma fīha isbāt el-melkeyya

A few useful notes:

• ال before د assimilates, so الداعمة sounds like ed-daʿma
• ث in Egyptian Arabic is often pronounced like s, so إثبات becomes isbāt
• الملكية is commonly pronounced el-melkeyya

So if you are aiming for Egyptian pronunciation, isbāt is more natural than the fully careful ithbāt.

Here الداعمة means supporting in the sense of:

• backing something up
• providing evidence
• documenting a claim

So المستندات الداعمة means:

• supporting documents
• documents that support the application/claim/request

It does not mean supportive in an emotional sense.

In administrative language, this is a very common phrase.

It is understandable and acceptable, especially in admin or form-related language. But a slightly more explicit version could be:

• المستندات الداعمة فيها ما يثبت الملكية

This literally means:

• The supporting documents contain what proves ownership

That version sounds a bit fuller because ما يثبت makes the evidential meaning very clear.

Still, the original sentence works, especially if the context already makes it obvious that these documents are being submitted as evidence.