I have not been to a universal park since the mid 90's and it was in California. I welcome all tips!
I was planning on buying the extra pass, I heard it was well worth the money. Since we will only have 1 day there I do want to make the most of it. I'll look into a hotel near Universal, maybe we will just do a night or two near there at the beginning or end of the stay. I am not opposed to spending a little more for convenience sake. We generally stay at Marriott or Sheraton properties near public transportation, but do branch out occasionally. We are planning on a few days in Singapore summer 2018 and if we do we will probably do US there too.
We travel pretty light, but I will be mindful of local laws about subways/trains and bags. I was planning on using the luggage forwarding service to move our stuff from Osaka to Tokyo. My sister isn't used to traveling and she will be alone with her kids so we are planning on meeting them at Narita. I have no idea how well she packs or how much stuff she is planning on brining with her but I figure the less bags we have to deal with the better. We will probably do the limo bus from Narita to our hotel .
I wasn't sure if you were thinking of doing AirBnBs since you might possibly have some hotel issues trying to get 3 children in a room with you. Some of the US higher end brands (like Marriott) will have larger rooms, but I'm not sure if they will allow 5 person occupancy. (and it varies by hotel/chain when a child counts as an occupant, it's really different from the USA, it can be as young as 6.) I've not stayed there but I would think for arrival, the Marriott in Tennoji is a decent location. It will be easy to get to from KIX and I've heard that area has really changed and become a lot more upscale. I admit, I usually just go to Osaka to visit friends, I prefer to stay in Kyoto. But if you like Marriotts I would look there and see if you would be able to find something that works. My husband has no vacation time for vacations, so most of my trips to Japan I've either been solo or more recently just with my daughter.
I know there is a Marriott near Tokyo Station. I've not stayed there either but I actually really like the Tokyo Station area. There are lots of places to eat, shop and it's super convenient for transportation. It's also a nice area to walk around. Tokyo Station/Shimbashi is my preferred area of Tokyo to stay in.
I've not used them, but there are also 1000 yen buses from near Tokyo Station Yaesu exit to Narita, which might be more economical for you when you meet your sister vs. trains or Airport Limo buses. (since you won't have luggage and are just going out to meet her) You can takyuubin to and from the airport. I usually takyuubin from the airport. To takyuubin to the airport you need to give yourself a 48 hour (I believe) leeway.
Since there is a delay with takyuubin, one thing you can do is: Stay X nights in Osaka, takyuubin your bags to Tokyo, take an overnight bag to an Osaka Universal Hotel and stay there, spend the day in USJ, either catch a late train to Tokyo or spend another night near USJ and then leave the next morning for Tokyo. When we went to USJ we only spent one night there and took a 5ish shinkansen from Shin-Osaka. But I wanted to try to get to my Tokyo hotel by 9. Your children are older than mine was.
I'd only been to US Orlando Pre-Island of Adventures, but my daughter was obsessed with riding the Jaws ride so we went to USJ. We stayed at the Hotel Universal Keihan Tower. The room was larger than I expected. We picked it for convenience and because it has an onsen on the top floor. I don't know if your family is interested in that, but you should at least go up since it's on the top floor and offers a lovely view of Osaka. We booked directly with the hotel and got a package that included room, park tickets, buffet breakfast, and one use of the onsen. The buffet breakfast was insane and had some unexpected offerings like: a chocolate fountain, cupcakes, off brand M&Ms, jelly beans, and cookies. I didn't get the NY theme as NYers do not generally eat cupcakes for breakfast. The Park Front is the closest hotel and there is also Hotel Kintetsu and Hotel Universal Port. Hotel Universal Port is the "furthest" away, but they were all SUPER close. The Keihan is not as fancy as the Tokyo
Disneyland Hotel, but is much cheaper, I paid 1000 yen less for my room, onsen, 1 day park tickets, breakfast and express passes than just the 1 night at TDL Hotel.
USJ seemed smaller than TDL and Sea, but felt less crowded when we were there. The kiddie rides are well done, my daughter loved the cars, but all of yours might be too old. I would recommend trying to buy your Express passes as soon as possible (like when you first arrive in Osaka, even if you won't be going to the parks for a few days) The passes do sell out. We had a 4 pass with different rides on offer than the current 4 standard and I think paid 9000 yen total. I had a friend in Japan buy my Express Pass for me and then I gave her the money back when I saw her. Like with TDR try to go on a week day. There is a USJ crowd calendar, it's all in Japanese but I would still check it out. We ate in Azzurra di Capri. We didn't have an advance reservation, we just walked in and had no problem getting a table. We ate at a normal time too, like noon lol
On crowded days there is some sort of timed entry to Harry Potter. I'm not quite sure how it works since we were there at a quiet time and just walked in. But even during quiet times, by the time we were done with lunch Jaws had an hour long line and I didn't even check Forbidden Journey's line vs. most of the kid rides never got a line over 20 minutes. But not having timed entry was great. We watched the wand show which was in Japanese and English and another show which also had English. At least in Harry Potterland, there was a lot more English than in TDR at shows.
It's not that USJ is that far from Osaka, it's not. It's just you almost always have to transfer at Nishikujo because there are few direct trains from Osaka Station. The Yumesaki line, which is the line for USJ runs about every 15-20 or so minutes from my memory. So it's short trips, it's just lots of waiting for your connection sometimes and like most theme parks you can get more done in the first hour the park is open. We weren't even being as time conscious as possible and had no problem riding Jaws and Flight of the Hippogriff within the first hour, but coming from further away just makes it harder to be there for that 9 am opening.
One super nice thing about USJ is there are actual physical waiting areas near where the ride starts/ends where non-riders can wait. My DD is still not 48 inches, but USJ had an enclosed waiting area she could sit in and watch Harry Potter movies while I went on the ride. Since we had two express passes for it, I got to go on it twice. They also had an enclosed waiting area for Jurassic Park. I imagine most rides with a height line have them. USJ rides are wilder than TDR rides. So if your children are not ride people, they might not enjoy it as much. We didn't go back this year because DD scares easily vs. DD loved TDR and keeps asking to go back.
