Hippowdon is the better choice. Not only does it have better healing other than Rest, (e.g. Slack Off) it also has a better defensive typing in Ground. Also, having a backup Sand Streamer is also great in Tyranitar, and Tyranitar is a great Pokémon overall. A set like this might work:
Hippowdon ( Physically Defensive ) @ Leftovers / Smooth Rock
Ability: Sand Stream
EVs: 252 HP / 4 Atk / 252 Def
Impish Nature
- High Horsepower
- Slack Off
- Stealth Rock / Whirlwind / Roar
- Yawn / Toxic / Stealth Rock
Stealth Rock is for hazards, and Roar / Whirlwind is to make great use of it by forcing the target to switch. Toxic is for stalling, and Yawn is to threaten switch-ins with Sleep. Slack Off is healing. Earthquake is great STAB, but hits all Pokémon, including yours, so I chose High Horsepower because since most of your Pokémon are weak to Ground a move that hits all Pokémon isn't great. The Rocks set is a lead but can be used anyways.
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Here's a Tyranitar set to do basically the exact same thing, but a bit better because it has Taunt.
Tyranitar (M) @ Leftovers / Smooth Rock
Ability: Sand Stream
EVs: 252 HP / 4 Atk / 252 SpD
Careful / Adamant Nature
- Taunt / Heavy Slam
- Stealth Rock
- Stone Edge / Rock Slide
- Roar
Taunt is to stop hazards on your field, and Stealth Rock is to create hazards. Roar makes use of it, and Stone Edge is just STAB.
> Hippowdon is mostly outclassed by Gastrodon because Gastrodon has Storm Drain, more resistances, and better coverage moves. Tyranitar wants Rock Slide over Stone Edge to hit both opponents and Heavy Slam over Taunt to cover stuff like Whimsicott, Diancie, Tapu Lele, and Nihilego. Sitrus Berry is a better item because Double battles are often too short for Leftovers and Smooth Rock to be effective.
Kick that Whiscash off your team. If you really want Paralysis, use something like Blissey ((DUU)) / Porygon2 (DOU) (don't take my word, I have no idea about if Blissey / Porygon2 is good in Doubles, but being bulky and having recovery is probably nice) or maybe just use Duraludon with Thunder Wave.
Gastrodon is great too, having nice coverage and access to Scald and Muddy Water.
Here's the Smogon set for it.
Gastrodon (M) @ Sitrus Berry
Ability: Storm Drain
EVs: 252 HP / 88 Def / 92 SpA / 76 SpD
Calm Nature
IVs: 0 Atk
- Ice Beam
- Earth Power
- Toxic
- Recover
Gastrodon holds a miniscule niche in DOU for its ability in Storm Drain, which allows it to redirect strong Water-type moves like Urshifu-R's Surging Strikes and Volcanion's Steam Eruption away from vulnerable teammates. Additionally, its typing and special bulk allow it to switch into strong Fire-type moves, such as Heatran's Eruption, and counterattack with moves such as Earth Power and Ice Beam. However, Gastrodon's typing makes it extremely vulnerable to Rillaboom's Grassy Glide. Additionally, Gastrodon is also fairly passive and has difficulty making a long-term impact on the game. Its effectiveness is also undermined by a lack of physical bulk, which also somewhat neuters its ability to counter physical Water-types that have neutral coverage. Gastrodon works best when paired with Pokemon that can take advantage of its ability to redirect Water-type moves. Diancie can gain some safety to set up Trick Room, while Fire types like Incineroar and Heatran also appreciate Gastrodon's ability to shut down threatening Water-type attackers. However, Gastrodon's 4x weakness to Grassy Glide means that it requires teammates that can switch into Rillaboom like Incineroar and Genesect. All in all, Gastrodon is overall a suboptimal pick that struggles to meaningfully benefit a team more than other options. Its weakness to some of the most potent Pokemon in the metagame means that facing a hard counter is extremely likely, and it doesn't provide enough utility for it to be worth it.