Hi I just want to know is this a pretty good team?

For blaziken replace slash with a strong fire move (flamethower is a good move).

Replace castform with a strong ice pokemon, spheal is a good pokemon.

No.

Here's some advice"
Your Blaziken: It needs to have a variety of different types with it's moves. It knows three different Normal attacks.

Gyarados: Train it more. Get rid of Splash and make it learn a variety of different types with it's moves.

The following paragraph is for if you don't wish to remove pokemon from your party.
For blaziken, get rid of strength and hyper beam, then bring back sky uppercut and teach it a flying move (I suggest arial ace if possible). Delete gyarados's splash for a strong move such as ice beam and train it untill it tries to learn more powerful assualts. I'm not sure what swellow can learn, so just train it up and give it some special attacks if it can learn them. Delete loudred's rock smash and astonish and train it up untill it learns good moves, and again, teach it special attacks if you can. I also don't know much about castform, so just raise it as you see fit. I'd also suggest using weak HM moves on a linoone, letting your fighters learn more powerful attacks and saving you money (due to pickup)
If you're willing to change your party here are some ideas.

1: Remove castform from your party. Although you can use its ability to your advantage, opponents have an easy time doing the same thing but more effectively than you.

2: Eliminate loudred, since normal is not good against any other type (except in resisting ghost moves) but weak against ones like fighting (defensively), steel (offensively), and unable to damage ghost types.

3: Either remove gyarados or be fairly cautious with it, since it can be quadruple-damage attacked by electricity.

4: Replace swellow with a creature such as skarmory or xatu, since the new type it adds lets the pokemon perform a wider range of moves.

5: Add pokemon with double types that both neutralize moves strong against the other one of its types (the best two are sableye and kingdra) or at least refrain from compounding weaknesses, and which permit the creature to learn move combinations that can do the most possible damage to any creature while permitting the user to survive for long periods of time.

Blaziken should have Blaze Kick, Fire Blast, Sky Uppercut, and then whatever you want for the other attack (but I recommend strength or rock tomb). For Gyarados anything but splash, it doesn't do anything! Get a stronger normal type attack to replace tackle and your good with gyarados. Swellow is great, but later it will learn a very strong attack called endeavor. Replace peck with endeavor. Replace pound with strength on Loudred and replace astonish with any other attack that's not normal type. I see that you've just gotten Castform so take away powder snow, but keep the other attacks. Put some strong attack with 10 or more PP and you've got the perfect team!