South being vulnerable will normally pass though those playing the old fashioned Lucas weak 2 or more modern aggressive pre-empting. Here is a great article on pre-empting by Brian Senior . Just need to agree with your partner and announce as weak if a weak 2M with one suit 5+ but alert if different from this.

West will bid 1♥ 

North is too strong for 1♠  or 1N and 2N is unusual NT. So will double.

East will make life difficult with 2♥ 

South will either bid 2♠ (a bit weak in HCPs but shape is great).

Over 2♠ , West will pass and North will bid RKCB.

South with 1KC will bid 5♣  (1 or 4)

North has all the key cards but South is a passed hand and to be sure of a grand, he needs south to have KQS, KHs and KCs = 11HCPS, so unlikely, so probably 6♠ is the safe bid. It is not good to bid a slam needing a finesse.

If South passes, North will either double again that is still takeout or bid 2♠ showing a strong hand and good ♠ s as he doubled. Over 2♠ South will raise to 4♠ and the RKCB will get them to 6 ♠ as before.

If North then doubles South will bid 4♠ (he denied with earlier pass so needs to catch up) with the same result.

As it happens, 2 finesses are needed and both work so 7♠ makes.