1. У неё болит горло — She has a sore throat
1a. У неё болят глаза — She has sore eyes

2. У них болят горла -- They have sore throats? OR
2a. У них болит горла -- They have sore throat? (can't visualize this, unless they share one throat )

Are the sentences above grammatically correct? I am sure #1 and #1a are OK, but not so sure about #2 and #2a.