37 years ago, I and a couple of co-workers were on a long term project in Los Angeles and spent a day at Disneyland in Anaheim. I was 30 years old at that point and while I could have taken 'a ton' of gear with me, I took only my Canon EF camera and FD 35-70 f2.8-3.5 lens mounted.
I found the 35-70 to be 'just right' in terms of size and weight to carry for 12 hours or so while walking and taking rides. Granted, that was a 'full frame' 35mm film camera back then, and you're taking a crop-sensor T5i.
With a 28-75mm lens, the field of view (angle of view) of that lens on your camera is comparable to what a 45mm-120mm produces on a ff camera. In other words, just a 'tad' wide angle and almost too much telephoto for what I suspect you'll be shooting. Most of the time, I suspect you'll be taking either family shots in front of something special or on a ride, or 'attraction' pictures (here's a shot of the xyz ride...). In both instances, I suspect you'll find the FOV of the 28 narrower than you'd like and you'll need to back up maybe 30-40 feet to get a shot of the kids in front of the xyz attraction, for example. Good luck getting a 'clear shot' where someone doesn't walk into the picture between you!
On the other hand, the taking the 18-270 gives you a wide-enough angle FOV (29mm equivalent), but at the 'cost' of f3.5 and slower, making low light work impossible without a flash. And on the telephoto end, far more reach than you'll ever need at Disney. Taking along the 50mm for low light work is a good idea. But the ability to 'quick change' lenses really is the problem, in my estimation. I think I'd rather carry a flash than an extra lens for easy accessibility. With a smaller size flash, I'd even leave it mounted to catch spur of the moment shots. But then, there may be instances where a flash isn't permitted, or, its use will completely wash out the colors of what you are trying to photograph.
In short, I think I'd go with the 18-270 and push up the ISO to 3200 for low light shots to avoid using a flash and still keeping a reasonable shutter speed in the 1/160th - 1/200th range to freeze human movement. If you're comfortable with higher ISO speeds on your camera, then do so. As I was shooting ASA 200 film at the time (ISO 200), I had several shots where I put the camera on a flat-topped trash container for 10 second and longer shots such as the Magic Kingdom Castle at dusk.
In my estimation, the biggest problem is how much weight you will be carrying and for how long. If you have the advantage of a baby stroller to carry things, all the better. If it's going to be over your shoulders in a backpack, for example, the weight will take its toll early on unless you are accustomed to carrying a backpack for hours and hours.
EDIT: Now that I'm older and wiser, I've picked up a fairly high-end point and shoot with full manual capabilities. As I've discovered, the Canon G15 is very capable in low light and takes pictures with a surprisingly good image quality, even in full Auto mode after dark! I'm going on vacation in a month or so and am leaning towards taking just the G15 instead of my full frame body and 2 lenses like I usually do. In short, as I'm likely the only person to ever see the pictures I take while on vacation, I'm willing to sacrifice an almost imperceptible IQ loss (after basic post processing work) to gain several pounds and 'pocket portability'. You may want to go that route as well.
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