kono hutatu no mondai ni ha kanren ga aru.

It is read:

この ふたつ の もんだい には かんれん が ある。

In normal Japanese writing, it would usually appear without spaces:

この二つの問題には関連がある。

この does not itself show singular or plural. It simply means this / these depending on what follows.

So:

• この問題 = this problem
• この二つの問題 = these two problems

In other words, the 二つ makes the phrase plural, so natural English becomes these two problems.

二つの問題 means two problems.

Here, 二つ is a quantity expression, and の links that quantity to the noun:

• 二つ = two things
• 問題 = problem(s)
• 二つの問題 = two problems

A useful comparison:

• 二つの問題 = two problems
• 問題が二つある = there are two problems

So when the number comes directly before the noun, の is commonly used.

二つ is the native Japanese -tsu counter, used for counting general things.

Since 問題 here means problems/issues, 二つ is a very natural choice.

A learner might wonder about 二問. That is different:

• 二つ = two items/things
• 二問 = two questions (especially numbered test/exam questions)

So if 問題 meant questions on a test, you might see 二問 in some contexts. But for general problems/issues, 二つ works very well.

には is に + は.

• に marks what the relation applies to
• は marks that whole phrase as the topic, often with a slight contrastive nuance

So the pattern is:

Aには Bがある
= As for A, there is B
= A has B

Here:

• この二つの問題には = as for these two problems
• 関連がある = there is a connection

So the sentence is structurally something like:

As for these two problems, there is a connection.

That is why English naturally becomes These two problems are related.

Because ある is being used in an existence pattern.

The grammar is:

Xには Yがある
= There is Y in/for X
= X has Y

So in this sentence:

• この二つの問題には = with regard to these two problems
• 関連がある = a connection exists

That means 関連 is the thing that exists, so it takes が.

Because 関連がある is a very common Japanese expression.

Literally, it means:

• 関連 = connection / relation / relevance
• がある = exists / there is

So 関連がある means there is a connection or to be related.

Japanese often expresses ideas this way, using a noun plus ある, where English might prefer an adjective or passive-looking expression.

Very natural equivalents include:

• この二つの問題には関連がある。
• この二つの問題は関連している。

Both mean roughly These two problems are related, but 関連がある feels like a set expression and can sound slightly formal.

They are similar, but not identical.

• 関連 often sounds a bit more formal and objective: connection, relevance, linkage
• 関係 is broader and more everyday: relationship, connection

In this sentence, both can work:

• この二つの問題には関連がある。
• この二つの問題には関係がある。

The version with 関連 sounds a little more formal, academic, or analytical.

Yes. Some natural alternatives are:

• この二つの問題は関連している。
• この二つの問題には関係がある。
• この二つの問題はつながっている。
  
  • more like These two problems are connected

Nuance:

• 関連がある = formal, objective
• 関係がある = common, broad
• 関連している = direct verbal form, very natural
• つながっている = more vivid, less formal

No. Standard Japanese is normally written without spaces:

この二つの問題には関連がある。

Spaces are often added only in teaching materials to make the structure easier to see for learners.