Also, checked bags should be on the carousel at LGA 15-25 minutes after arrival, very unlikely more than 30.
Thunderstorms likely to be the biggest concern. If there is the potential for a delay, the DL agents in MCO should be able to put them on a flight into JFK assuming the schedule works (often JFK and LGA flights are at similar times) and there are seats. Even without a delay they may be willing to do that, it’s definitely worth asking, note their bags would be checked all the way through to GVA in that case.