Tyranitar-I would put Earthquake over Pursuit.
Sandslash-Very good moveset.
Starmie-I wouldn't worry about Rapid Spin on Starmie, there are better moves for it, Thunderbolt would work nice instead.
Porygon-Is that a typo, or are you really intending to use a Porygon instead of Porygon2? Anyways, if you plan on using this team for competitive battling, then I hope that you are using Porygon2!! Your moveset is pretty good, but I think Curse would fit nicely into your moveset. Curse+Double Edge+STAB is pretty nice. Also, Ice Beam wouldn't be a terrible choice over Thunderbolt either, especially since you don't have any Ice moves on your team.
Miltank-Ok, but Curse would prolly be the best option for the last move.
Skarmory-Not bad, but Sand Attack doesn't work all that great IMO. Curse would be better.
Overall: You have a lot of Pokémon that are good Cursers, Tyranitar can make good use of Curse, but it can also get by without it. You may want to take Curse off of Tyranitar, and replace it with Flamethrower/Fire Blast, to give your team a little more variety, as some of the other Pokémon in your team are a little more dependant on Curse then Tyranitar is. Also, your team has a 3x weakness to Fighting types (Tyranitar, Porygon, and Miltank) and Grass types (Tyranitar, Sandslash, and Starmie.)