We are a family who used to eat 2-3 TS meals each day in Disney's restaurants, and I'm going to say your itinerary is too ambitious, since you are a first timer, with two small children. You will spend all of your time in restaurants - will you have a car? Using Disney transportation to get to resort restaurants is going to eat up even more time.
We have done this as well, but we are DVC members, and my kids have been to Disney many, many times since they were 10 months old, so missing park stuff wasn't an issue. You, on the other hand, are first timers, and you will spend all of your time in restaurants. We have since cut this pattern of eating out, as not only is it too expensive, but it takes up too much time in the day, as Disney restaurants are much too busy nowadays due to the dining plans.
We used to be able to get in and out of a character meal within 1 hour, even with 2 babes - characters were not rushed, food was refilled, and service was fine. Not anymore though, thanks to massively busy restaurants - although you are going at end of Sept., but is there
free dining during that time? Character meals are also very chaotic and the food/service has really gone downhill, so they will take up precious time in your day, waiting on characters and for things like the check. Doing 2 of them per day, is really going to be a lot, IMHO.
You really have no choice as you are doing DxDP for 5 days - 5 days for a first trip is not a lot of time at all, so by the time you take out all of your meals, you have more like 3 or 3.5 days, as your kids can't stay up too late, as they are very young, plus, at that time of year, Disney does not stay open very late at all. We also don't feel that Signatures are worth it, but you may have to consider a 2 credit Signature as well, just so you don't lose your credits.
So, you need to consider the following when making your decision:
- nap schedules of your kids
- transportation to and from the restaurants
- eating schedules
- park schedules
I wish you luck in figuring out your itinerary. May you have a magical trip, Tiger