I've taken the train from NYC to Orlando a few times and my sister has taken it from Philly to Orlando also a few times.
This is a grueling trip, especially in coach. Even with a roomette--and I would never even think about doing this again without a room or roomette--it is still a tedious, aggravating trip. And since there are 4 of you, you would have to get two roomettes. I don't even think a room would be big enough for 4 people. Now we're talking big bucks.
Why is the trip grueling? Because it goes on forever, there is all but no interesting scenery, there's no decent food on the train (you have to bring your own if you value yourself and your family), the train can stop for a loong loong time--hours, sometimes--and you can be many many hours late for your scheduled arrival.
The last time I took the train they were stopped for so long somewhere in Georgia, iirc, that they were threatening to put everyone on a bus--a BUS--for the rest of the trip. At that point I was almost in tears. Fortunately, they rescinded this idea and got the train moving again.
Passenger trains in the US have to make way for freight, which has the right of way. In none of my several Amtrak trips to Orlando have I ever arrived early or on time. Always late. Sometimes incredibly late.
Also . . . you will get to sleep on the train in coach only if you are wildly lucky or don't need quiet or even semi-quiet in order to sleep. Your coach car will be filled with children, babies, people who aren't wearing earphones but are listening to/watching something on their phones or tablets, people walking back and forth, conversations, phone calls, etc.
My sister thought she'd have a relatively pleasant trip and would save some bucks once and took coach from Philly to Orlando. She had zero sleep and was miserable the entire time. She paid an exorbitant price to get a roomette on the way back.
If I were you, I'd drive. That is definitely the cheapest way for you to do the trip. Either that or start pricing out other airports. You don't have to fly out of Philly, do you? There are a zillion flights to Orlando from Newark, which isn't that huge a drive from Philly.
