I can save you a whole lot of time and say Wyches are not viable. Dying by droves to Bolters is a bad place to be for an Assault unit that doesn't even put out a whole lot of damage against common enemies. You're looking at a unit that is outright worse than Genestealers in the Tyranid Codex, and Genestealers were an almost surefire way to lose a game. So, you will have to go into it with that in mind, your unit is going to die horribly more times than it will accomplish something, so your army needs to maximize on their death and take extra steps to make them annoying.
Your initial concept is flawed. If you Deep Strike them, they're dead. They'll be surrounded by whatever gun is closest and blasted off the board. They are T3, so a Large Blast of S6 or higher will outright kill almost every single model it touches. They won't get FNP from S6 or higher. Consider a Raider or a mess of Reavers to deliver a squad. Both have benefits. Raiders get a 3+ Jink with Night Shields, which lets them serve as an Assault boat. Your models can Assault directly from it without standing around with their thumbs up their butts. But Raiders are also bad, so there's that. Weak things with limited firepower. Reavers only carry five models, but three Reavers means 15 Wyches, and on top of that, three Reavers. Reavers with two Splinter Cannons are good units and again, you can charge right out the back of them. They're weaker and only protected by a 5++, which is why you need many of them so some survive the drop. Alternatively, look at Ynnari from Gathering Storm 2. You lose Power from Pain, but gain Soulburst, which allows out of sequence attacks when a unit dies. Having multiple small units allows Soulburst to really shine because remember, a unit may only Overwatch once per turn.
Now your questions. Did you pay for your codex or did you find it online? Because I found mine online and there is a very clear part missing from a failure in the file where it would say Artifacts of Cruelty, but since I don't use Haemonculi I never noticed. If you have found it online, take a look at a paper codex to double check. If you have a paper codex in front of you, I don't know. I'm not seeing anything in Haemonculus Covens to grant them Artifacts either so I have to assume my own book is wrong or the youtubers are wrong. I'm going to bet my file is faulty though.
2: Ally is a word and it means almost nothing anymore. As you build your army, 'ally' only comes in to play when you determine the relationship between Detachment A and Detachment B. An Allied Detachment is just a name of another specific Detachment but the term ally and Allied Detachment are completely seperate. You will be allied to whatever you bring as another Detachment but you can pick any Detachment that exists to add into your army, no matter the faction, ally level or type as long as all the restrictions are abided by.