Since im feeling generous id explain it to you, whether you believe what the manga says or still stick to your fantasy is up to you. Ill explain it that even you will understand
Hiruzen started with shadow shuriken technique and oro used edo tensei;
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The first coffin came out first because they were summoned according to when they were hokage (hashirama was first). Hiruzen at first thought oro used a coffin to block his shrunken when he thought "To use a summoning as a shield". He finally got was going on when he thought"these summoning are". Notice that the first coffin was already out and so was the second (second hokage). ;
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He then went on to say i must do something about the third one. When the first coffin was revealed he didnt know what was going on. Its after the first was revealed did he get the hint, but at the that time the 2nd coffin was more or less out. Common sense says the last coffin which hasnt surfaced yet, he would try and stop that one because he has the opportunity to, unlike the first 2. Why would he not want to stop the third when he had the opportunity to but more importantly fighting 2 hokages is no small feat, anybody in that situation would try and minimise the work load and fight 2 instead of 3, not hard to wrap around your head.
That coffin failed anyway, but neither oro nor sarutobi knew why. Hiruzen thought he stopped it but he didnt. Anyway he then went on to say
"of all people, for him to summon those two" (hashirama and tobirama). This alone should tell you that, he wasnt scared of any coffin, if anything its those 2 he was scared of;
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