Or can I do both in same week? (normal EP and heroic EP)
You can do both 
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From Wod and on, different raid difficulties are on different lockouts. I think anything before MOP shares the same lockout.
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ICC though Cata raids if you did a raid on 10 man it would have a different lock out then 25 man but yes the heroic and norrmal for these raids within the size setting were the same. (Uldular and Firelands do not count anymore due to TW to this rule . Ulduar has one diff and I have not tested to see if Firelands is more like WoD and beyond lockouts)
Raids from naxx to Throne of thunder have the “you can only do this raid once regardless of difficulty / player size”.
SoO onwards you can do normal, heroic and mythic, as blizzard used SoO as the testing grounds of the WoD raid difficulty system.
Note: LFR has its own lockout, even for raids from Dragon Soul to Throne of Thunder.
If you do 10 man ICC, you can not do 25 man ICC. it was a change blizzard made in Cata, as they made it that 10 and 25 man modes dropped the same loot for cata raids onwards
During Wrath you could do 10 man and 25 man separately as they had different loot.
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You are right, I completely forgot SOO was a thing. In my mind MoP ended with ToT for some reason.
Can confirm that Normal and Heroic Firelands raid are two different lockouts. The 10 or 25 man versions do not matter as I did the 25 man of both normal and heroic, then tried to go back in on 10 man mode normal, it was cleared, and 10 man heroic, it too was cleared as I took out every mob around.
Mate, did you really need to necro a 5 year old thread that got answered when it was made?
Also Firelands is now has a flexible player size due to it being a timewalking raid. Likewise for Black Temple and Ulduar. No such thing as 10 and 25 mans for Ulduar and Firelands anymore.