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Even if you assume you can have a 'wish with conditions' (which seems suspicious), the price to pay is out of line.
If the wish with condition is valued at the highest cost (kill mother), the price to pay (toenail) is too low for killing a Z given Miluki's past example (assuming whoever he's trying to kill has to be easier than killing his own mother by any measure).
If the wish with condition is valued at the lowest cost (kiss by Alluka), the price to pay is way too high for such a trivial task.
If the price to pay is the average of the two (the price still seems too low) , then it is too easy to cheat the system with the example I described (just list a lot of conditions, as long as you're able to control the condition to get the wish you want).
Being able to command Gotoh and Canary wouldn't even be enough to get past Tsubone based on what we know of the characters so far. Obviously Tsubone isn't going to take an order from Killua, and presumably Amane won't either.
Of course she will! She's a butler. Despite not allowing Killua to cross tha family rules, she HAS to obey him. And so does Amane. He is their boss, and unless he crosses the line, they'll be under his command. Tsubone was even making sure Alluka would obey Killua, she does not intend to break the chain of command.
As for the conditions, Milluki had no idea it was possible, and I'm sure only Killua so far knows about how they work. There might be further rules for it to work properly and avoid cheating the system, and I'm sure we don't know all about Alluka yet. Every chapter something new is revealed.