Pronunciation. From BBC and Cambridge.
A question from Svetlana in Kazakhstan:
Could you help me to explain difference in pronunciation of two pair words - there're, they're and there'll be, they'll be? Dictionary pronounces separate words they, there, are and will. However, in real English speech you use contraction. These contractions are usually unstressed, so it's difficult for me to define difference.
Em podrieu ajudar a explicar la differència en la pronunciació de les parelles de paraules  there're/they're and there'll be/they'll be? El diccionari ofereix la pronunciació per separat però a la conversa real l'anglès empra contraccions. Aquestes contraccions no tenen accent cosa que en fa difícil la diferenciació.

Hello Svetlana – this is a great question as, like you said, it's almost impossible to find the answer to this in a dictionary or grammar book. You're right – we use these kinds of contractions all the time when we're speaking and because they're not 'important' words like nouns or verbs, they tend to get mumbled a little bit and it’s difficult to hear how they are said.

If you try and pronounce any of these contractions slowly, you can make out the differences between them:

there're        /ðɛərə/        
they're          /ðeər/
there'll be      /ðɛərl/ 
they'll be    /ðeɪl/

But of course, when we're speaking normally we don't say them slowly and in fact, the two pairs of words you're asking about end up sounding almost exactly the same. Let's try putting them into sentences so you can hear them in context:

She said there're going to be about a thousand people there.
I hope they're all going to bring something to eat!
If not there'll be a lot of hungry people.
I expect they'll be so busy dancing they won’t think about food.

Can you hear that the first two words sound a bit like 'there' /ðərə/ and the second two words sound like 'thell'/ðɛərl/ . Listen again.

Because, as you said, they are unstressed, the pronunciation of the second syllable in each word almost completely disappears.

One last thing – one of the contractions you’ve mentioned is only really used when speaking, while the other three are used in informal writing as well. Do you know which is the odd one out? It’s there're - the contraction of 'there are'. It's quite uncommon to see this written down unless you are trying to write exactly like we speak, for example in direct speech in a dialogue.

I hope this answers your question. Remember to practise saying them within whole sentences rather than as single words as it's much easier to make the pronunciation sound natural.