I used to have half of my team very similar to yours...
I recommend getting them to level 60 if you want to beat the E4 easily.
I use to train them on 1 Island, there are a few trainers outside the spa, that's a good spot, I spend most of my training there.
Also you can go through all the citys and routes challenging all the trainers, some of them will very usefull since they have leveled up their team, some of them haved evolved their pokemon or even add more members to their parties, that way your team would level up relatively quick.
Hope this will help you