Question Help with sentences in this context [Manga/MC's thinking about his battle strategy and how it will affects to people lives]

[zeroh4nter]

Context : MC and A-san have thought out a strategy/plan to defeat the enemy. Now MC and A-san is marching on the main road ,with their army and the armed people/militia of their town ,toward enemy's castle.Much thanks if anyone can explain to me the correct meaning of his thoughts here o/

A-san「この作戦で、大丈夫かな……」 "Hey I'm wonder will everything be alright ,with this plan/strategy..."

MC: 「大丈夫だってば。二人でしっかり考えた作戦だし……きっと上手く行くって」 "I told you,it'll work.It's a strategy that we have thought out thoroughly together... I'm sure things will go smoothly."

そうは言うけど、もちろん自信なんかあるわけがない。 I said that to her,but of course I don't have any confidence.

人事を尽くして天命を待つ……なんて言うけど、掛かってるのはみんなの命だ。それじゃダメなのはわかってるけど……。 We did what we can,now we'll just have to wait for fate to decide...or so I'd like to say, but what I'm dealing with here are everyone's lives.I know that I should not have that kind of mentality but...

MC（……俺のミスで人が死ぬっていきなり言われても……こんなの、どうしろっていうんだよ） (...I mean,even if I'm suddenly being told that people died because my mistake... What am I supposed to do about it ?)

These bolded parts are the 2 sentences I'm not quite sure about what he has been thinking.
If my understanding were wrong please correct me ,thank you !