1) Stop selling it to me. 1) Stop selling it to me.

More common: • Stop trying to sell it to me. • Stop trying to get me to buy it.

1) Stop selling trying to sell this (fruit) to me. 1) Stop trying to sell this (fruit) to me.

Your sentence would also work, it's just slightly less natural. 'fruit' would typically be left out in everyday speech.

Have you ever caughtseen me buying any other kind of fruit? Have you ever seen me buying any other fruit?

I eat apples solely. I eat apples solely.

Suggestion: I only eat apples.

I only eat apples solely. I only eat apples.

There're different degreshades of grey between them. There're different shades of grey between them.

I’m having trouble imagining a context where “between them” would sound natural in your sentence. What does “them” refer to? My suggestion: There’re also many shades of grey.

There' are different degrees of grey between them. There are different degrees of grey between them.

There're isn't common

5) I've been practiscing this same movement for hundreds of hours, yet I’ve failed to see any progress. 5) I've been practicing this same movement for hundreds of hours, yet I’ve failed to see any progress.

We spell it “practicing” in American English.

5) I've been practising this same movement for hundreds of hours, yet I'm faileding to see any progress. 5) I've been practising this same movement for hundreds of hours, yet I'm failing to see any progress.

You would be frustrated too if the bootyou were oin the other footmy shoes. You would be frustrated too if you were in my shoes.

I’m having trouble imagining a context where “if the boot (or shoe) were on the other foot” would sound natural here. The standard definition of this idiom is: “The roles of people in a situation have been reversed, such that the advantage has shifted to a party which was previously disadvantaged.” The last part is important: this idiom is used when someone who was weak now has power.

3) I thought if one of my family was a millionaire, I would have known that, but it turneds out they've been keeping it from me all these years! 3) I thought if one of my family was a millionaire, I would have known that, but it turns out they've been keeping it from me all these years!

It’s very difficult to correct this without knowing the full context, including how long ago you discovered they’d been keeping it from you. The above correction assumes you just recently discovered the deception. The following is also possible, if you discovered the deception a while ago: “I thought if one of my family were a millionaire, I would have known that, but it turned out they'd been keeping it from me all those years!”

3) I thought if one of my family wasmembers were a millionaire, I would know that, but it turneds out they've been keeping it a secret from me all these years! 3) I thought if one of my family members were a millionaire, I would know, but it turns out they've been keeping it a secret from me all these years!

Again, your sentence is good, my corrections just add a little bit of clarity/natural-ness

They think everything is either white or blackblack or white. They think everything is either black or white.

We always say “black or white” in this order.

2) I think if one of my family were a millionaire, I'd have known that. 2) I think if one of my family were a millionaire, I'd know that.

2) I think if one of my family members were a millionaire, I'd have known that. 2) I think if one of my family members were a millionaire, I'd have known that.