Tbh we can't help so much if you don't tell us what tier are you interested in, but I'll do my best giving you generally useful advice.
First of all, let me introduce you the amazing world of Scald. It's one of the best Water STABs ever, wich not only has a Base Power similar to Surf and more accuracy than Hydro Pump but even a 30% chance of burning to punish common checks for Water types like Dragon, Water and Grass types lacking Water immunity. It's also a single target move, so it hits harder than Surf in Doubles. This said, you should use Scald instead of Surf for Kingdra and Pelipper. If you want to play in Doubles Pelipper can use Brine to take advantage of its mates' strenght and his slowness to KO opponents' pokèmon.
Now my2cents about Rain teams. Drizzle is absolutely enough to set the wheater: you don't need to use Rain Dance. Your team on paper seems very good having two Rain abusers and two pokèmon able to deal with other Rain teams, but you picked not so good pokèmon. While Pelipper is the best Rain setter and Kingdra the best Swift Swim abuser in SM Goodra, Toxicroak and Heliolisk can be outclassed by other pokèmon with same roles depending on the tier choosed. MGardevoir isn't a common mega for this archetype because MSwampert and MScizor are preferred, while the first one benefits more from Sand.
Lastly I want to say that MGardevoir hasn't the bulk needed to be a good Wish user, while Toxicroak lacks SpA to use a mixed set.
First of all, let me introduce you the amazing world of Scald. It's one of the best Water STABs ever, wich not only has a Base Power similar to Surf and more accuracy than Hydro Pump but even a 30% chance of burning to punish common checks for Water types like Dragon, Water and Grass types lacking Water immunity. It's also a single target move, so it hits harder than Surf in Doubles. This said, you should use Scald instead of Surf for Kingdra and Pelipper. If you want to play in Doubles Pelipper can use Brine to take advantage of its mates' strenght and his slowness to KO opponents' pokèmon.
Now my2cents about Rain teams. Drizzle is absolutely enough to set the wheater: you don't need to use Rain Dance. Your team on paper seems very good having two Rain abusers and two pokèmon able to deal with other Rain teams, but you picked not so good pokèmon. While Pelipper is the best Rain setter and Kingdra the best Swift Swim abuser in SM Goodra, Toxicroak and Heliolisk can be outclassed by other pokèmon with same roles depending on the tier choosed. MGardevoir isn't a common mega for this archetype because MSwampert and MScizor are preferred, while the first one benefits more from Sand.
Lastly I want to say that MGardevoir hasn't the bulk needed to be a good Wish user, while Toxicroak lacks SpA to use a mixed set.
