sono simai ha me ga yoku nite imasu.

姉妹 is read しまい and means sisters.

It specifically refers to female siblings. In this sentence, it means the people being talked about are sisters, not just siblings in general.

その means something like that / those, but in Japanese it often refers to something already mentioned or known in the conversation.

So その姉妹 can mean:

• those sisters
• or sometimes just the sisters if they are already understood from context

It does not always need to sound as distant or specific as English those.

は marks the topic of the sentence.

So その姉妹は means:

• as for those sisters
• speaking of those sisters

The sentence is setting up those sisters as the main thing being discussed, and then it says something about them.

Here, が marks 目 as the thing that has the quality being described.

The structure is roughly:

• その姉妹は = as for those sisters
• 目がよく似ています = their eyes are very similar

This is a very common Japanese pattern:

• topic: a person or group
• subject: a body part, feature, or possession

So instead of saying their eyes directly, Japanese often says something like:

• as for them, eyes are similar

を would not work because 似ている does not take a direct object here.

It is simply understood from context.

Japanese often leaves out possessives like:

• my
• your
• his
• their

when they are obvious.

So その姉妹は 目が... naturally means:

• as for those sisters, their eyes...

Japanese does not need to say 彼女たちの目 unless it wants to be especially explicit.

No. Here よく does not mean often.

With 似ている, よく means:

• closely
• very much
• a lot

So 目がよく似ています means:

• their eyes resemble each other closely
• their eyes are very similar

This is a different use of よく from the common meaning often.

似る is a verb, but when talking about resemblance, Japanese very often uses the ている form: 似ている.

That is because resemblance is treated as a state:

• someone is resembling
• something is similar

So 似ています is the natural polite form for saying that something is similar / resembles something else.

似ます is grammatical, but it is much less natural for describing someone’s current appearance in a normal sentence like this.

That is a very good question.

Yes, 似る often appears in patterns like:

• A は B に 似ている
  = A resembles B

For example:

• 妹は母に似ている
  = My younger sister resembles my mother

But in this sentence, the comparison target is understood rather than stated.

その姉妹は 目がよく似ています means that the sisters’ eyes resemble each other. Since that comparison is clear from context, Japanese does not need to say it explicitly.

So this sentence is not missing anything unnatural. It is just leaving the comparison target implied.

Japanese nouns usually do not show singular vs. plural clearly.

So 目 can mean:

• eye
• eyes

In this sentence, the natural English meaning is eyes, because we are talking about a facial feature the sisters share.

So 目がよく似ています is best understood as:

• their eyes are very similar

A very literal breakdown is:

• その = those / the
• 姉妹 = sisters
• は = topic marker
• 目 = eyes
• が = subject marker
• よく = closely / very much
• 似て = te-form of 似る
• います = polite いる, making 似ている

So the structure is roughly:

• As for those sisters, (their) eyes closely resemble each other.

That body-part structure is very normal in Japanese.

Not necessarily.

This sentence specifically says that their eyes are similar. It does not automatically mean that their whole faces or overall appearance are similar.

So the nuance is more limited:

• maybe their eyes have the same shape
• maybe they have a similar expression around the eyes
• maybe that feature especially stands out

If you wanted to say they look alike in general, Japanese would usually say that more directly.