4. their vs there vs they're: their indicates possession (It is their car), there indicates a place (He is over there), they're means they are (They're late)
5. to vs too: to is a preposition (We are going to France), it is also used with full verbs (He wants us to listen), too is another word for also (They will visit them too)
6. who's vs whose: who's means who is (Who's that girl he's talking to?), whose indicates possession (The girl whose dad is over there is my niece)