We were pulling out of the parking lot at a local college where my 3 older girls take art lessons. The saw two girls walking to their van and Cassia says, "They must be sisters." Anna pipes up, "They get along really well. They must be friends."
Meaning #1 - They're not only sisters, but friends, as well!
Meaning #2 - There's no way 2 people who get along that well are sisters!