"I have sons and daughters."
Translation:Tengo hijos e hijas.
That's what I enjoy about duolingo, you have to find out for yourself by trial and error, just as you would in the real world. It's immersive learning, which studies show creates stronger neural connections in the brain. There's an entire internet that explains the rest anyway.
It is grammatically correct, but that doesn't make it "natural" if you understand what I mean. Let's take English, there are many phrases in English are grammatically correct, but "unnatural" in everyday speech. It's the same with Spanish. "Tengo hijos e hijas" is "unnatural." You would rarely, if ever, hear it from a native Spanish speaker.
The personal "a" is not normally used with "tener", there are cases where you would, but it's more common to not have the personal a with it. http://spanish.about.com/cs/grammar/a/personal_a.htm
Yes and it's similar in English with "a/an". They both mean the same thing, but for grammatical/pronunciation purposes "an" is sometimes used in place of "a" if the noun that follows begins with a vowel (an umbrella). Same with "y/e" if the word that follows "y" has an "ee" sound, the "y" changes to "e" to avoid having the same sound back to back. http://spanish.about.com/cs/grammar/qt/y_o.htm
True, and some native Spanish speakers might say "y" instead of "e", but when it's written it should still be "e" in this context. That's why I said that for it to be grammatically correct, it should be written with an "e", whether or not you do it is technically up to you, most people probably wouldn't even notice if you said "y" rather than "e", but just know that "e" is the correct choice in this context, just like how it should be "an apple" even though we sometimes may saw "a apple". http://spanish.about.com/cs/grammar/qt/y_o.htm