Ramzawing
Instead of "heavenly hallows" why not "Lively Hallows" since your basing them of the "Deathly Hallows" and instead of a crown as one them why noy go with Merlin's wand/staff or even better make it Avalon the scabbard of Excalibur. Make the Holy Grail an heirloom for the pendragon family or have it in a vault in Gringotts but can't be unlocked unless he's worthy and of a certain age (obviously need's to have pendragon blood) and do something similar to the sorting hat when a gryffindor is in need it summons "Sword of Gryffindor" but instead of the sorting hat and "Sword of Gryffindor" replace them with Holy Grail and Excalibur. But this is your book do with it what you want
Honestly, as long as you don't make it clishe and/or generic, and you actually put some work into the personality of the protagonist and the antagonists and you keep it consistent, immersive and believable(as in the villain will start WW3 cause the MC stepped on his shoe or some **** like that) it will be fine. If you're going to deviate from the original story, then the keyword in that will be consequences, what will happen if something you're implementing, simply doesn't make sense in the HP universe? Just keep that in mind, that only applies if you're planning to keep the story at least true to it's franchise, if you're going to create something new and different then don't mind that but the other 3 keywords still apply. Consistent - what I mean by this, is that the personality, interactions between character and etc... must be "consistent", for example having the MC extremely angry or in a rage and then suddenly someone comes in(usually a girl or lover) and says one word and he immediately becomes a puppy dog that forgets how to speak(it's crazy the amount of times I've seen this in a novel...however it simply doesn't happen or make sense and is frankly BULL****), essentially keep the story at a level where the situations are at least believable, and this links with the next keyword Immersion - This is fairly ****** to stay true to, as long as the story is "believable" and the events are easy to understand, even if the story is fantasy so it's quite hard to link it to real life, as there is usually no common sense in said type of genre, as long as most of it is understood or related in someway to the "real-world", then it would be acceptable. Believable - I've used this word a few times already, because it functions and reacts best with the other keywords(think of it as a compound substance-made up of more than one element). This one is easy make it BELIEVABLE, don't have interactions or responses between characters that make no sense(e.g. MC meets Boy A talks with Boy A for five minutes... Boy A gives his mom to MC for him to marry...catch my drift yes?) Obviously there's more but this is acceptable for now.
glad to see you back, and im looking forward to you coming back, was thinking along with excalibur and the holy grail, the last one could be a ring, or a necklace, small, but powerful, cause the deathly hollows follow that setup, yours could as well, 2 noticable things (weapon and cloak) and the third unnoticable( like a royal signet ring type thing). either way, im looking forward to it. oh, and you could call them the Pendragon Pieces, or something along those lines. either way, glad your back mate, and im looking forward to how it turns out.
Just make cool items that are inheritence items from Arthur and Merlin for the pendragon bloodline that way you can add whatever you want without limits, you can even make some kind of artifact from the original knights of the round table :) no need to limit things by name or by comparing it to deathly hallows (since they're lame) :p welcome back!