okay, let's do this. I'm assuming you're playing singles. You mentioned anything goes, which makes me think you're playing singles. If you're playing doubles, correct me and I'll rewrite this.
first, primarina. Moonblast is superior to dazzling gleam in every way, having more base power and having a fairly high chance to drop sp. attack. Having both liquid voice hyper voice and sparkling aria is extremely redundant, since they both accomplish the exact same thing. The only difference is that hyper voice doesn't cure burn, which is a problematic side effect of sparkling aria....at least, it would be a problematic side effect if any pokemon on your team knew moves that caused burn. I'm actually going to suggest a move on another one of your pokemon that can cause burn, but even then, the likelihood of this effect screwing you over is low. Therefore, just use sparkling aria, and scrap hyper voice, and by extension liquid voice, altogether. Replace it with hydro pump, you definitely want that brute force for when sparkling aria isn't strong enough. You could replace ice beam with psychic, but it's not really a huge deal. Also, if you're running choice scarf, you want a timid nature and 252 speed EVs instead of HP EVs. I heavily question the point of a choice scarf on a slow mon that works best as a wallbreaker; choice specs would be far superior. You definitely want EVs in speed for a specs set too, since wallbreakers want to outrun the walls they are trying to break.
meowth is difficult to work with, since it's...well, meowth. And this isn't little cup. It's so frail that even with eviolite, it's bad at taking hits, so I'd replace it with a sash. I guess that's your call though, eviolite isn't completely without merit. Its offensive stats are awful too, so the only thing I can see it doing is annoying things with its speed. Perhaps hypnosis/taunt/u-turn/foul play. Knock off, toxic, fake out (if you use fake out, go with focus sash, max attack EVs, and technician), and body slam are fair options too. I don't see a reason to run protect on this thing, but if you did that, there's no reason to run detect too. Detect can fail if protect was used the previous turn, and vice versa.
you could use a curse set on miltank, but I think it's a poor idea, since its special bulk is so average (this is important, since it's the stat you're not patching up with curse; it's a curse user's more vulnerable side). If you want to use curse, move the defense EVs to sp. defense for this very reason. If you want to use a more practical set, the current nature and EVs are fine (I'd move the 4 attack EVs to sp. defense or speed, but that's really minor). Rest is a subpar form of recovery in most situations, and it's redundant with milk drink. Either toxic or thunder wave (you might wanna replace body slam with either return or seismic toss if you run twave) would be best off replacing rest, and heal bell would probably be best replacing curse. Normally I'd suggest stealth rock on miltank, but I'm not going to here, for reasons you'll see in ten seconds.
piplup is obviously hard to work with too, though it has more reasonable bulk than meowth. Therefore, I think eviolite would be better suited on it, with EVs poured into bulk. Since its stats are so poor, it should probably be your team's stealth rock user, since stealth rock isn't impacted by low offensive stats. Other status moves are also good for this reason. I'm feeling that stealth rock/defog/yawn/scald would be the ideal moveset since it's so stripped for options. If you're using rapid spin on donphan, you can use toxic over defog, since the purpose of both moves is to remove hazards the opponent sets. Rest/sleep talk/stealth rock/scald could work too, maybe. You could possibly use whirlpool over scald if you want.
the EVs and nature on donphan are fine, but the item and moveset have to go. Donphan is a tank, which means it's designed to take hits and dish them out; life orb is contrary to the former goal, so you'll want to replace it with an item that doesn't eat up its HP, probably leftovers. Earthquake is a necessity, for its sheer power. You can keep either stone miss or head smash, preferably the former, since head smash also clashes with donphan's goal to take hits. Roar isn't a bad move per se, but it tends to be more useful on more passive pokemon. You can keep it if you want, it could be a useful way to help stop setup sweepers from crushing your team, but donphan's decent power is likely sufficient for that job already. Knock off, ice shard, rapid spin, and maybe play rough, seed bomb, and a few other moves would be fine options for its moveset.
ursaring is far too slow to run a belly drum set. It doesn't even have priority. I really suggest a quick feet moveset for this one (if you didn't know, quick feet boosts speed by 50% when statused). Your team has literally no fast attackers on it (because let's be real, meowth isn't hurting anyfin), and with quick feet, max speed EVs, a jolly nature, and a toxic orb, ursaring reaches a speed equivalent to about base 106 speed. That's enough to outspeed mega pinsir, charizard, and more. It's not super fast, but it's respectable. As for the moveset, return, earthquake, crunch, and swords dance would definitely be ideal, although you could substitute earthquake for either cross chop or close combat if you so desired.
um, that's about all the advice I have for this team. Honestly, besides primarina, every pokemon here ranges from terrible to mediocre, so don't expect amazing results even with my advice. If you need any further explanation, let me know.
