I have done all 3 that you have mentioned - Jingle, Jingle Bam (outside), Frozen (both inside and outside), and I have done the garden view in MK (although for HEA, not for Holiday Wishes).
I have had a stroller for all 3. For Jingle, Jingle Bam parking was outside the party. For HEA you brought it inside the covered party area but outside where the tables are (if that makes sense). You then picked your stroller up and brought it with you when you went outside to the gardens. Frozen the answer depends on if the party is inside, or outside. If it is outside, then similar to HEA, you bring your stroller in the roped off party area but it is placed to the side away from the tables. You then grab your stroller after Illuminations and will park it outside the Frozen attraction while you are on the ride. If the party is inside, then you find a spot to park it somewhere in Norway. You probably could theoretically leave it there until after you ride Frozen but what all of us seemed to do was grab our strollers after eating as we were heading to the roped off Illuminations area. We kept them with us while watching Illuminations and then parked them in front of the Frozen ride while we rode.
Out of the 3 parties I enjoyed HEA the least and wouldn't even begin to consider it during MVMCP. Now while I did do HEA fairly recently (May) the food offerings changed (last month I believe) so I can't really comment on the current food. I know many people were complaining that the desserts weren't anything to write home about. I didn't think they were bad. My daughter, who is 5, loved that she got to drink champagne (sparkling apple juice in plastic champagne type glasses). There is no alcohol during the HEA party. When we arrived we were brought to a table. I didn't quite understand if they were actually assigned or if they just randomly placed people when they arrived. After eating/drinking you will be escorted over to the gardens. I did enjoy the space we had while being out in the gardens. There was enough of room that my daughter made friends and they were playing tag and toss the stuffed animal. You are really close to Tinkerbell if she flies. However, I personally did not like the view for HEA. Now I'm not someone that normally gets a spot for HEA really early and I still manage to get a better view than what we had during the dessert party. If it was only fireworks then the spot would have been great, but since HEA is also heavy projections on the castle that's where the view falls short. There are trees and light poles that partially obstruct your view. I actually found that the further back in the gardens you go the better the view. Since I normally see HEA multiple times when we visit Disney I may do the party again since I know one of the other nights I'll have a better view but honestly I wouldn't upset if I never did the party again. That being said, I wouldn't even consider it during MVMCP. There is soo much going on during the party that it is not worth the time it takes to do the party. As well as you have already spent a lot of money on party tickets, I can't see spending more on a lackluster party.
I enjoyed the Jingle, Jingle Bam party. Since I was outside, the seating was right outside the Chinese Theatre. There is alcohol. The food was great. There is assigned seating for the food portion so no worry about the time you arrive. There was a surprise guest (Goofy Santa) that you get to meet and he does have a photopass photographer. The party is smart when it comes to meeting Goofy. In order to maximize your party time, you are actually given a slip of paper with a time to meet Goofy. That way you only have max 2 groups in front of you so the wait is minimal. There was something about that party that really put me in the holiday spirit. You are given holiday themed fireworks glasses and a souvenir ornament. When you are done you will be escorted to the reserved space to watch Jingle Jingle Bam. You need to stand in that viewing area. The only negative for this party is the viewing area is rather close. The best viewing (to try and see everything that is happening on the the Chinese Theatre) is if you go to the back of the viewing area. If I had known that I probably would have gotten there a little earlier. Overall, I would do the party again.
The Frozen party is my favorite party. I definitely enjoy it more when the weather cooperates and it can be held outside but inside wasn't bad at all. Food and alcohol are great. You are given special fireworks glasses (I've received 2 different ones). I have NOT had a photopass photographer at either party. There is assigned seating. If you are outside tables are small (5 people) and if you are inside the tables are larger. You definitely will have to share inside. Outside it depends on the number of people attending. We lucked out that our part of 3 was by ourselves when we were outside but that doesn't always happen. If you are outside you will stay seated at your tables to watch Illuminations. What I really enjoyed is you can continue to eat and drink until Illuminations ends. If the dessert potion is inside then you will be escorted to the same viewing area where the outside party would have taken place. However there will not be any tables and you will stand at the rail to watch Illuminations. Since the inside party takes place only during inclement weather (or too cold), for this party you are basically all moved at once. Then of course after Illuminations your guides wait until the mass of people have passed and they escort you back to the Frozen attraction. At that point the only people in line for it are those that attended the party so the wait is really short. The upside for me is that is one attraction that I don't need to worry about a FP for. While this hasn't happened to me, there is a potential con.... I have read reports of people that did the party and the Frozen ride was down. Instead they were given a FP to either Soarin' or TT (I can't remember which). The big complaints are that both of those have a 40" height limit so that doesn't work with little ones. That's also not ideal if it's your last night at Epcot. I haven't heard of this happening in quite a while but be aware it's possible it could occur. As one last point, while I know there is tons of places to watch Illuminations with a good view, there is something about the reserved party spot that I felt it was one of the best views I've had of Illuminations.