Трое в лодке, не считая собаки
Russian number's system is a tricky one but this will impress you!
That is why I decided to explain this topic of Russian grammar to prove that Russian does not like blind spots in the language and gives you names and definitions for everything.
If you would like to speak about the number of people connected in your mind in a certain group (by their interests, by profession or possessions, etc.) you use such collective numbers:
2 - двое
3 - трое
4 - четверо
5 - пятеро
6 - шестеро
7 - семеро
8 – восьмеро
Normally we use these collective numbers from 2 up to 8. After them we use Genitive plural form.
For example, let’s compare two sentences:
Три студента вошли в класс.
Трое студентов сидят в классе.
In the first sentence we mention how many students have entered the class.
But in the second sentence we emphasize that 3 students are sitting at the class together so they are waiting for the same lesson. The lesson or the same topic for discussion makes these 3 students the one group with similar interests.
If you are talking about your family you cannot say:
Мы в семье четыре.
You have to say:
Нас в семье четверо.
Because all members in your family are connected to each other.
Also when you are talking about children you should say:
У меня трое детей (Нет: У меня три).
Be the way when you are talking about a group of people which consists of both men and women, then two forms are possible:
1. В комнате три сотрудника = В комнате трое сотрудников.
The same if you are talking about babies or baby animals.
1. У меня два малыша = У меня двое малышей.
2. У меня пять котят = У меня пятеро котят.
If you still think that Russian is very complicated and without logic you should change your perspective of view and you will find the great explanation for each fact in Russian language.
Wish you good luck and see you at LAE language school in Kiev!