Not quite, it would be more like stating that your sisters are right now at your place.
"есть" is a form of the "to be"-verb, stating existence. That's how you describe possession in Russian to give new information.
However, есть is dropped when you rather describe properties or quantities (I have a clever sister/I have many sisters). Which makes it a bit different from English "have", which works in both cases,
There is a rule for female plural nouns: basically you just change "-а" in singular female noun to "-ы", and "-я" — to "-и".
But for male nouns there is no specific rule. There are some basic rules though which says that you cant use "ы" after letters "ж", "ш", "ч", "щ" and sometimes "ц", so in these cases you have to use "и" in others - "ы". upd. yeah and singular male nouns ending with "-к" will end with "-и" too when plural.
And there is another rule for neutral plural nouns: "-о" in singular form becomes "-а" in plural, and "-е" becomes "-я" with an exception of "яблоко - яблоки".
Bonus level: There are some words that do not have singular forms, e.g.: "деньги", "ножницы", "очки"...
It is phonological constraints and spelling conventions. Right now you should know that whenever you make a new form, К is always used with И rather than Ы (кошка→кошки, мальчик→мальчики)
- nouns like мама, девочка, кошка, тётя, земля produce a plural using -ы/-и
- nouns like компьютер, мальчик, актёр, велосипед usually produce a plural by adding -ы/-и
- but some of them have a plural ending in stressed -а/-я (доктор→доктора, поезд→поезда, учитель→учителя)
- nouns ending in -ь mostly produce -и plurals; only a few masculine nouns are the exception (see above)
- neuter nouns ending in -о/-е typically end in -а/-я (though, яблоко becomes яблоки)
- there are exceptions with weird forms (e.g., мать→матери, дочь→дочери, брат→братья, друг→друзья, стул→стулья, сын→сыновья, ухо→уши)
- 10 neuter nouns in -мя have a separate pattern with -ен (имя→имена)
The choice between ы/и or а/я is predictable and seen through the whole paradigm — basically, the noun either has "palatalised" endings in all forms or non-palatalised endings in all forms, including the base form.
However, not all consonants can combine with ы and я, which causes some confusion at first.
Yes, sure. This is what makes Russian hard for a beginner who wishes to speak without any trouble whatsoever. There is a limited number of frequent patterns, however.
Here is the whole paradigm, ordered as Nominative, Accusative, Genitive, Prepositional, Dative, Instrumental:
- singular (NAGPDI): сестра́, сестру́, сестры́, сестре́, сестре́, сестро́й
- plural (NAGPDI): сёстры, сестёр, сестёр, сёстрах, сёстрам, сёстрами
It is a preposition (literally, "at, near"). Russian commonly uses it to express possession through existence ("At me, there are sisters").
This preposition combines with the Genitive form:
- мама → у мамы, сестра → у сестры
- актёр → у актёра, брат → у брата, окно → у окна
- лошадь → у лошади
- я → у меня, ты → у тебя, вы → у вас, мы → у нас
- он → у него[nʲɪˈvo], она → у неё, они → у них (and кто → у кого)