They'll

[svetlana14]

Does the speaker say they'll (help set)?

14:48. He pronounces they'll so stuttering and fast that I cannot follow either of the following two ways Americans say: /ðeɪl/ as Oxford Learners Dictionary suggests.

3:05 where an American native speaker claims that typical American pronunciation is "thell".

 

[emsr2d2]

In the first video, there's no stuttering. He says the three words pretty fast, particularly running "help" and "set" together but yes, I heard "they'll help set" and the pronunciation of "they'll" was pretty much as the guy in the second video demonstrates.
In BrE, both "they'll" and "there'll" sound much the same ("thell" with a hard "th"). That's not the case for AmE speakers who use a rhotic "r".

They'll help me.
There'll be fifteen people there.
They'll be here at six.
There'll never be another actor like him.

 

[5jj]

I heard "they'll help set" and the pronunciation of "they'll" was pretty much as the guy in the second video demonstrates.
In BrE, both "they'll" and "there'll" sound much the same ("thell" with a hard "th").

What do you mean by 'hard "th"'?

For me, the first sound of "they'll" is /ð/, the voiced dental fricative of the, this, that, mother, breathe, etc.