Okay, buckle up.
I've never been to Jiko, but from what I've heard - it serves up some delicious food in a really wonderful, fantastically themed setting. Plus, the fact that it's in your hotel is a huge benefit. You could eat at any hour, stay as long as you want, and then head upstairs and go to bed.
Raglan Road is a little different. For one, it's a Table Service, compared to Jiko's Signature designation. Jiko will be a little pricier than Raglan Road. Jiko is also a quieter, more subdued setting; whereas Raglan is loud, boisterous and fun. Ask yourself - would you rather have a nice sit-down meal and chat with your family, or slug some drinks back, clap and cheer and enjoy some music and Irish step dancing? I think it'll come down to your family's preferences and what kind of meal you're looking for.
On the other hand, Raglan is about a 20-minute drive from Animal Kingdom Lodge. So, keep in mind that it would be a 40-minute round trip. Let's say you wrap up dinner at 10ish - then you wait for a bus and by the time you get back it'll be around 11-11:30pm. Whereas if you finish eating at Jiko, you can be in your room sleeping by 10:15pm.
As for the parks...
We do Magic Kingdom every year. We're not afraid, whatsoever. For whatever reason, Magic Kingdom doesn't get too crowded until 10am. After that, it's mayhem. Magic Kingdom will have a morning EMH. Typically, we arrive on Christmas Eve. We'll do a nice sit-down restaurant and then call it a night. We'll try and shower the night before so that we could wake up, change and get out. We'll get up Christmas morning around 6:30am-6:45am at the latest. We'll be down at the bus stop by 7:15am and make it to MK by 7:30am-7:45am for the last half hour to 15 minutes of the morning EMH. We'll usually jump on Space Mountain, as the wait is under 20 minutes. After, we'll jump on the Jungle Cruise - as the wait time usually jumps up after the park opens. We'll usually have FP+ for Buzz (we always have a competition for highest score), Thunder Mountain and Haunted Mansion. My mom isn't a big thrill ride person. In Christmas, we like to stay together, so we usually book rides that we can go on together and save 7DMT and other, faster rides for other days. Space Mountain is easy enough to get on before or right after RD, so we don't pick it. Out FP+s are usually done by 1pm. By then, the park is very crowded. We usually call it a day by 1pm or 2pm. We'll head back to the hotel and relax for a while before heading out to dinner. For dinner, we usually do a Signature such as Narcoossee's. This year, we're changing it up and going for a different restaurant.
Last year we did Il Mulino on Xmas Eve and it took us a while to get back to the room. We champed it out, as we always take a midday break, but if you plan on doing Magic Kingdom in the morning and staying there all day, I would stick with Jiko and stay at the resort.
EPCOT is really cool during the holidays. There's plenty of delicious foods and snacks, and storytellers from each pavilion's respective country that tell guests about the country's holiday traditions. It's nice to snack and drink around the world and learn about each country's tradition. I've never been to EPCOT on Christmas, so I can't really comment on the crowds. I will say this - if you're just going for the World Showcase, the crowds don't really have much of an impact (unless it's NYE.) EPCOT is very spaced out, so it tends to absorb the crowds pretty well. Soarin' will be at a 120+ wait time and Test Track will be at 90+ minutes, but for food and exploring each country, I'd totally recommend it! You can even afford to sleep in a bit on Christmas morning and then head there. I've been to the parks 6 of the past 7 years. I've been to Magic Kingdom on Christmas and EPCOT on NYE. I've never been turned away. Guests staying onsite benefit when it comes to phased closures. It would have to be a Phase 4 closure for onsite guests to be turned away - and if it's at Phase 4, you don't wanna be in there, anyway!
Hanging at the resort and relaxing all day wouldn't be the worst thing. We stay at Disney from December 24th through January 2nd. By December 28th or 29th, we start to get a bit burnt out. By the end of your trip, you may not want to deal with the crowds and the rides and you may have seen and done everything already. The fact is, MK doesn't do anything special on Christmas Day. The parks don't do anything on December 25th that they don't do on December 23rd or 24th, so you really wouldn't be missing much. There's definitely a special feeling - you're in Magic Kingdom on Christmas - but other than that, there's nothing special.
So basically - yes the crowds get crazy and the wait times are astronomical. But the crowds don't get crazy until around 9am - giving you plenty of time to get some stuff done if you arrive for the morning EMH or rope drop. I think most people either sleep in, eat a nice breakfast on Christmas morning, or spend the morning opening presents. I also think that most guests on Christmas Day are off-site guests and guests from the area. They probably hit a lot of traffic and it takes a bit longer to find parking and take the ferry over from the lot.
I'm not sure how bad the crowds will be the first half of your trip.
MVMCP ends on the 18th (I believe), but there is free dining. When we arrive on December 24th, it usually doesn't seem too bad.