After two passes, South in position 3 should try to do the maximum to bid to make it difficult for West. 

Here with 10 HCPs, 5/4 in the two longest suits, whilst this does not meet the rule of 20 for opening many will open 1♠ with this hand as there is an easy rebid of 2♥ though the vulnerbility is adverse. In this case it is a good decision.

West will probably overcall 2♦ and North with 4 cad support and a maximum for a pass will jump to 3♠  that will be passed out.

If South passes West will bid 1NT that is a great contract for E/W

After 2 passes East will bid 1♠ with an easy rebide of  2♥ .

West will bid 2♣ s and East will show shape 5/4 with 2♥ .

East has a choice between 2 and 3♠ s. With a maximum for a passed hand can bid 3♠  to invite 4♠ . East is relatively balanced and no extra values so is likely to pass.

Some Wests with 10HCPs and a six card suit may open 1♣  and rebid 2♣. 

After 2 passes East opens 1♣  then North overcalls 1♠ . 

East can do a forcing bid either double to show values and support for other suits. Alternatively bidding 2♠  to clarify the hand could be useful. West with a ♠ stop could bid 2 or 3NT to show values and a ♠ stop, though no ♦ stop.

The alternatives are to for East to raise 1 to 3♣ s . 

This hand will cause a great debate.

Those who say you should not bid a weak 2 with 4 cards in the other major.

Here is a link to an interesting article and hands from Larry Cohen https://www.larryco.com/bridge-articles/weak-2-bids which is a great resource for lessons and suggestions. Though it is based on American bidding systems.

A poor 9 HCPs with the singleton K♦ suggests it should be a weak 2 or a pass.

If West passes North will bid 1NT that will be passed out and is a great contract for N/S

The question is whether North should open 1NT or 1♦  with a safe 2♣ rebid.

The doubletons have stoppers and NTs will be a better contract, if they make, so many will open 1NT, but a good percentage will open 1♦ .

Here is a good article that discusses the 1NTbalanced hand shape from Larry Cohen again. https://www.larryco.com/bridge-articles/when-does-a-notrump-bid-show-a-balanced-hand

West opens with 1♥ , the top of 2 5 card suits.

Some Norths, opposite a passed hand may jump to 3♦ though 2♦ will be more often bid.

Over either 2♦ East will bid their 6 card ♠ suit and West will show support by bidding 3♠ .

North may want to risk 4♦ but with 4 good ♦ s 8HCPs opposite an opening hand East will double for penalties or may bid 4♠ . Without North bidding East is likely to pass.

East will open with a weak 2♥ s.

South will probably bid 3♦ that will be passed out.

After East opens 1♦  south can bid 2♦ that is Michaels bid showing 5/5 in ♠ ♥ s.

West passes and North bids the lowest of the two equal suits - 2♥ s which will be passed out. Vulnerable East will probably pass as bidding 3♣ is risky, but less risky with N/S bidding the majors.

South has a poor 10 HCP hand with values in 6 card suit. The Q doubleton in ♦ s is not worth 2 HCPs so many will bid 2♠ s.

If South bids 1♠ with the intent of bidding 2♠ s.

West may risk an overcall of 2♥ s.

Then North has a difficult bid, but bidding 2♠  showing support with a 3 card suit is probably the best answer and better than passing or doubling. This is likely then to be passed out.