Yes, they can manipulate imagination and your memory.  But they cannot manipulate your will.  And they can only do anything so far as God allows, which St Paul tells us, God will never allow a temptation beyond your strength.

They can't read our minds or access our memories but they can interpret with a preternatural skill our moods by watching us.  They are the masters of "microexpressions".  Then they manipulate our surroundings to generate their desired reaction in us.  They have a better memory of past situations they have observed.  They share intel with other demons.  And they also have a network of human toadies to accomplish their goals.  That's why it's so important to stay away from unholy spaces as much as possible.  And have no contact with humans that consistently do intentional mischief.  These are my personal beliefs.

Yes, agree.  But with regard to memory, they don't need to access OUR memory, as they know what happened to us all our life (and have a better memory of it than we do). 

If I had a goldfish, and I recorded its whole life, I don't need to access the goldfish's PERSONAL memory, I just look at the recordings, to know what happened.  And then I can manipulate/lie to the goldfish, by suggestion, that x happened, even though y actually happened.  Studies show that eyewitness accounts are very unreliable because memories can be distorted and, especially with the passage of time, human memory is often horrible on details.

All this assumes that we have a guardian angel and...that we have a devil angel...assigned to us at birth.  The guardian angel part is near-de-fide.  The devil angel is a theory, but it makes sense to me.  That would explain how the devils manipulate memory; they can't get inside our head, but they've been recording us our whole lives.