I am a bit confused over something, can someone help!?

So this week James and Chelsia are HOH.

I think they will put Matt and Natalie and Amanda and Alex up.

Then its POV and out of the hat is Sheila and Adam.

Sheila and Adam win POV.

Sheila and Adam decide to take Amanda and Alex off the block.

James and Chelsia put Ryan and Allison on the block.

I get that.

So in two weeks lets say Ryan and Allison and Sheila and Adam have been evicted.

Matt and Natalie win HOH. They put James and Chelsia and Sharon and Joshuah up.

Adam and Amanda must play POV.

James and Chelsia win POV. Use it on themselves.

Adam and Amanda then must go up.

So what happens the week after? If it is exactly the same?

Because thats only going to be week 5/6 of a 13-week show...

Do we think they split from their couplings?

After that, one down to three it could continue as in the other seasons. There is a final HOH comp and the winner decides who is evicted and who they face in the final.
I think they might split up the couples long before this point though.

I think you've got it wrong.
If Sheila and Adam get POV, then they choose who to take off. Or put on. Chelsia and James, as HOH only get to choose who to put on the block first. It would have to be Sheila and Adam who decide to put Ryan and Allison on.

HOH decides the replacement nominees as well as the original nominees. However, they can't nominate those removed (obviously) or the veto holder