Shēng sounds like shèng here.
Is it so? Can you hear it too? I know bù sounds like bú here, as it should.
You are right. It is pronounced incorrectly
For certain phrases or words tones can be changed or it could also be the accent/dialect of the speaker
You can either be ni or ni men
Ni men means you-all or y'all.
This sentence is quite easy!
are not: 不是
Has this app with speaking exercise or can you write in chinese or pinyin?