From the owner's manual (p. 3-34):
"LATCH anchors have been provided in your vehicle. The LATCH anchors are located in the left and right outboard rear seating positions. Their locations are shown in the illustration. There is no LATCH anchor provided for the center rear seating position."
I don't see a LATCH weight limit published publically for Hyundai. However, the standard minimum weight cut-off is at 40 lbs (weight of child, not including the seat). The official NHTSA standard is apparently 65 lb including the weight of the seat. I foundone site that recommends 48 lbs as the cut-off for the weight of the child (justmommies.com
And the YF is the model generation code which Hyundai uses. (The previous generation of the Sonata was NF). It is similar to the "E" codes which BMW uses in the development of each of their vehicle generations.