Do you say like that as below and is one of them grammatically correct?
Let's I will do that.
Let me you all/all of you do this.
Let's I will let you do this.
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I don't think any of them are correct. They are certainly all very awkward.
The contraction let's means "let us." So the first one should be "Let's do that." Meaning "Let us do that." Or possibly you mean to say "Let us agree that I will do that." It is not clear what you intend.
The second one confuses me. I think you want to say "Let us agree that either I will do this, or you will do this." You still need to decide on which of "I" or "you" will be doing it, but this sentence asks to agree that one of these will do it.
The third one could be "Let us agree that I will let you do this." Or maybe just "I will let you do this."