Mohammad, you are bringing up an issue that even native-English speakers sometimes don't realize- the essential nature of punctuation and how it is instrumental to sentence clarity. Most people are familiar with periods, spaces, and commas, but there are over a dozen punctuation marks that you can use to make your sentences clearer and consistent with your intention. As suggested by the other answers, there are many things you can do with your original sentence and example sentences to make them clearer.
Is it a List of Three (3) , Example of Two (2), of Just Two (2)
The first thing is that the sample sentence you cited (the "flatfish sentence") is unclear. Unless you know that sand dabs and flounders are flatfish, or you looked them up, you could have equally assumed that the author was listing three separate things. For example:
"Buildings that are over 80 stories tall, Cityspire Center and Metropolitan Tower, have an additional structural aspect when engineered."
Based on how you analyzed the flatfish sentence you would be mistaken to assume that the two specifically named buildings are two in the category of "buildings over 80 stories tall". However, they are not- both buildings are under 80 stories tall. It could be a list of three things (buildings over 80 stories, Cityspire Center, and Metropolitan Tower) that share an engineering characteristic. Similarly, the manner in which the "flatfish" sentence is structured, it could properly be interpreted as a list of three things (the family of flatfish, sand dabs, and flounder). Part of this problem stems from English not having an "ironclad' rule for lists and conjunctions (and, but, for, nor, or, so, yet). For example this:
"Members of the flatfish family, sand dabs and flounders, have an evolutionary advantage over many colorfully decorated ocean neighbors in that they are able to adapt their body coloration to different environments."
may or may not mean the same as this:
"Members of the flatfish family, sand dabs, and flounders, have an evolutionary advantage over many colorfully decorated ocean neighbors in that they are able to adapt their body coloration to different environments."
What Does it Mean?
You also don't know if the flatfish sentence means to say any of the following about the evolutionary advantage:
- that it is a feature shared by the flatfish family, sand dabs, and flounders (three things);
- that it is shared by all members the flatfish family, for example sand dabs and flounders; (many things of which two are named);
- that it is a feature of sand dabs and flounders, who are members of the flatfish family; (two things from a class of many).
I googled the sentence you cited and read the passage from where it was excerpted. The original passage means to discuss an evolutionary advantage that only sand dabs and flounders- have not all flatfish. However, you can't immediately tell from the sentence as originally composed. That sentence should have used additional punctuation, words, or word order to delineate that sand dabs and flounder are a subset of the flatfish family and that only they have the advantage:
" Sand dabs and flounders, members of the flatfish family, have an additional evolutionary advantage …"
Dolphins, Friends, and Family
Once you know what it is you want to say, you can then construct a sentence that represents this clearly and concisely, with as little ambiguity as possible. You could leave it up to the reader to properly interpret what you mean, but it really is up to you to tell people what you mean as clearly and concisely as possible. In the original sentence you cited, we can add "dolphins":
"Sand dabs and flounders (members of the flatfish family) and dolphins have an additional evolutionary advantage..."
"Dolphins and two species in the flatfish family (sand dabs and flounders) have an additional evolutionary advantage..."
In the case of the sentence referencing your family, the same suggestions I gave prior would help. However I still think you should re-think of removing some words. It is true that your mother, father, and sister are family members, but you may want to consider the redundancy of including both "my family" and listing the individual members. The sentences:
"My mother, father, sister and my friend are going to the restaurant."
"My family and my friend are going to the restaurant."
are equally clear, without the redundancy of "my family" or the list of individual members- after all it is this combination that is causing your problem. (This would be a different case if "your family" could change in meaning with a word modifier.)
I know this answer was long, but I hope it demonstrates why constructing sentences is more than just about grammar. It is also about using punctuation, word choice, and word placement, to convey the intended meaning to your reader or listener.