If I could know what level your Pokèmon are, that would be great, anyways, continue on. :)
The one way I do my training is where I level up a certain Pokèmon to a level, and when it reaches the level I want it to be, I level the rest of the team up. It takes time, but sometimes that's how you get evolutions.
Another way I do it is by what I call step leveling. You raise one Pokèmon's level, you raise all of the teams levels, just by one. This is quite easy since you have some under leveled Pokèmon, so I would recommend this one. However, sometimes they might grown one, two, or even three levels, but you still have to raise them up to that level, no matter what happens to it.
If you where playing ORAS, you could stock up on Blissey Bashes in Secret Bases. This is the most easiest leveling up technique ever, and it only costs 24 hours of waiting, depending on how many you do. All you need to do is scan a code and wait a couple of days. This takes time to process, but it is the most fastest way to leveling up, because Blissey provides so much EXP points.
Some of these ways are good, depending on how high your Pokèmon's level are and what the wild Pokèmon's level are.