Hippowdon: Nice set, but you can max the SpD. Give him a Careful nature(+SpD, -SpA) and give him max SpD EVs. I do this because mainly Hippowdon tends be weakest to Water/Ice. His defense will still be high, so don't worry. Also, don't the Females look better? Otherwise He's good.
Tyranitar: It's true, he's unexpected. He's going to be really strong banded, and though he has some weaknesses he gets that nice Special Defense boost in the sand. You could consider Pursuit>Crunch if you have fleeing psychics to kill. I like him.
Lucario: Looks great, but there are a couple of things to do. Why Hasty nature? He's not given any SpA moves, so just make it Jolly(+Spe, -SpA). You could also give him Hi Jump Kick instead of Close Combat, as it's more powerful and it has annoying stat reducing effects. Just hope you don't miss. ;)
Reuniclus: I love seeing people use this guy now, because he's just so AWESOME! But, there are a couple of things on your particular reuniclus to change. Ok, you might not need leftovers because you can recover by yourself. I'd reccomend the Life Orb for some nice power with no recoil. Energy ball is probably better than Focus Blast, because you'll run into Gastrodon/ Politoed more often. Give him a BOLD nature(+Def, -Atk). He doesn't need the extra SpD because he'll still have an awesome Special Defense once he has 1 or 2 calm minds up. Besides, most of his major weaknesses are physical (Bug, Dark). Looks good, and he'll do good on your team if you use him right.
Landorus: Looks like the set I have, only this one is scarfed. You could consider the expert belt since you have some nice coverage in your moveset. If not however, you could make this guy Adamant for more attack power. Now that I think of it, if you wanted more attack power...
Landorus-T @Choice Scarf
EVs: 252 Atk/ 252 Spe/ 4 HP
Nature: Adamant(+Atk, -SpA)
I've never tried this guy out, so I don't know how well he'd work. He'd certainly be quite strong though. If he doesn't work, you can always go with my advice at the top. Who knows? Maybe he could be the next big thing!
Gastrodon: Good, UP's set works well, as you'll soon find. However, there are still some tweaks to be made to this gastrodon. Since he has stockpile, and will wall most attackers, give him some Special attack so he can actually do something. Try this EV spread: 252 HP/ 128 SpA/ 84 Def/ 44 SpD. Also, Ice Beam > Earth Power. Why? You may ask. Dragons. Especially flying dragons. They can dragon dance you and stay practically unhurt. Give'm ice beam and they won't be able to set up.
Good luck with the Sand.
A wise man once said: "With great power comes great responsibility..."