Well I can't have the noble phantasm do as it says. Getting your master to help you shouldn't give you the ability to (for example) use Blood Clarent Arthur, Mordred's Phantasm, because it's a literal personification of her rage towards her father not in innate part of Clarent the sword. It doesn't make sense. Archer even states using Excalibur at a similar level inside of unlimited blades works might end up killing him. In her story Chloe summons Excalibur to use against morgan Excalibur but it only manages to draw the battle out. It's arguable if the blast was at it's full potential. 

It was probably just a giant prana blast on both ends. If it copies a weapon's design, and allows Chloe to use an approximate ability to the noble phantasm that's fine. Worse comes to it she gets a sword she can swing around like Clarent, or Gae Dearg. Maybe one can use prana slashes like Excalibur, or some sort of minor curse that replicates the original to a lesser degree. But using/copying Galatine shouldn't give the ability to just sit in the sun for a few hours and gain Gawain's boosts.

I'd rather not take the risk all the same. I'm trying to work with you here and get a servant that doesn't render any other character inert because they could potentially just have their skills taken by Chloe if she likes them. It prevents enemies from being effected because Chloe can't possibly rip away say Caesar's incitement if he's trying to kill her. At the same time it basically gives her the chance to steal instinct, and mana burst from Arthur which are two incredibly dangerous skills since Arthur is a top tier servant.

 Astolfo less so but the potential is still there. I also intend to bring along other npc servants to aid us from time to time so things like Mind's eye (which she's already giving up just for this skill), or presence concealment can be added to that list. So she could just end up with skills she ditched on top of skills she could gain otherwise.

The trust thing doesn't need to go directly towards her master. It can be Leon, Arthur, Astolfo, or his master. Or any other ally.