This is going round and around with nonsense, so I'm just going to explain it plainly.
In order to do get the Weekly Challenge remnant, you don't ever have to do Silversteel. All you need to do is:
1) Botany Center, Titan Chamber, Hall of the Keeper, Hall of the Templar (all are super easy nowadays and people do them all the time, just remember mechs for BC and TC)
2) Do daily dungeons in the cross server. Focus on Brood Chamber, Warped Citadel, Cathedra Cliffs and Halcyon Hills (but in all honesty, doing all available dungeons is a good idea)
Doing 5 or so dungeons will net you those last 2 Weekly Challenges, giving you 6 WC completed, giving you the remnant.
Remember that, even if the dungeon is not part of the Daily Challenge for that day, it will still drop the remnant. So doing the following dungeons once a day will net you remnants:
-Heaven's Mandate*
-Cold Storage*
-Drowning Deeps
-Sandstorm Temple
-Ransacked Treasury
-The Shadowmoor
-Dreamsong Theatre
-Brood Chamber
-Warped Citadel
-Cathedra Cliffs
-Stonescale Passage
-Hangar Zero
-Halcyon Hills
-Naryu Sanctum*
Please not that the dungeons marked with an asterisk are not currently being nerfed for the event. While doing HM and CS are still very easy to do, Naryu Sanctum might be a bit too much for you and can be skipped. Also, with the dungeon nerfs, it's entirely possible to solo a good chunk of these dungeons. DD, ST, RT and TSM should all be doable. DST, BC and WC are possible with enough DPS. CC and H0 can be done easily enough with any party while essentially ignoring mechs (though melee characters might have some issues in H0 when the sensors come up). The only nerfed dungeons that will still require some mechanics are Stonescale Passage and Halcyon Hills.
For Stonescale Passage, you need to remember that both final bosses must die at close to the same time or else the party will wipe. Pay attention to chat and communicate when to kill or hold DPS. The player in Soul Separation cannot see both health bars, so you need to make sure to tell them when it's okay to kill their target. More likely than not, it will take them longer to kill their boss, so communicate with the rest of the party to stop DPS (usually something like "stop out" to indicate to everyone outside of SS to stop attacking) when the boss has less than 10% HP (and the boss inside SS still has more than 10%). Ultimately, the main thing to remember is communicate and kill both bosses at the same time. It's not actually that difficult.
For Halcyon Hills, only the first boss has any real mechanics to deal with... but again, if you don't do them, it's a wipe. Upon starting the fight against this boss, he'll go into the sky and begin throwing lightning AoEs at everyone in the area. The safest thing to do is to move sideways (left to right/right to left) to avoid the areas the lightning will hit, then when they do hit, reverse direction and go the other way (it's not necessary, but it keeps people from running into each other's areas and potentially getting them hit by the attack meant for you). While you're dodging lightning AoEs, 3 players will get a gold target symbol appear under their feet. After about 1 or 2 seconds, one of the monkeys surrounding the area will throw a peach/rock. Those who have the target symbol must use a block skill to catch the peach. If you successfully caught the peach, keep dodging lightning until the boss begins preparing a big attack. When he does, press LMB to throw the peach at him, knocking him down to the ground where you all can attack him (hit him with everything you've got, because after one spin attack he'll do, he's going to go back on his cloud and the mechanic begins again). If nobody knocks him off his cloud, his big attack will wipe the party. However, that's all you need to know for mechanics in Halcyon Hills. Also... remember to interact with one of the 6 large jugs in the map (1 for each party member) before reaching the final boss. You need a jug before fighting the final boss in order to complete the Daily Quest in order to get the remnant.
I've already gone long enough explaining all of this to make things easier, so I'll leave it at that. You can work out getting the other remnants on your own. There's 1 week left. After that, they'll probably put keys for NCoin in the Hongmoon Shop if you're desperate.