See if you can find a weather forecast that has "hour by hour" temperatures. I think either weather.com or accuweather.com has that feature. Then you can tell if it will be 60 degrees at 8:00 a.m., or 46 degrees at 8:00 a.m.
I would pack a variety of clothes for each person, including a warm jacket, gloves, and a hat. I was at WDW in October 2009, and we had both record-high and record-low temps, all on the same trip. I had plenty of shorts, sleeveless shirts, and sandals, but not enough warm stuff. Because it was pretty breezy on my Epcot day, I was pretty darn cold - searched all over for some knee-socks (finally found something at the Japan pavilion). I was reluctant to pay WDW prices for a warm jacket/sweatshirt two days before I left, so I just layered and toughed it out. It was such a surprise to have such cold weather in mid-October-- I had checked the forecast before I left, but only looked out seven days. Things can change very quickly!