1♠  - P - P - x

P - 2♦ - P - 2NT

In fourth "balancing" position many people play 1NT as 11-14, so double followed by the lowest NT shows 15-16.

East may overcall 2♦ but is probably a bit weak in HCPs for this, but those playing weak jump overcalls may bid 3♦  which makes it difficult for West - pass or 3NT?

NTs will often make 9 tricks as the natural standard lead of the 10♠ s (top of internal sequence) of longest suit) allows West to develop the ♦ s

4♠ -P-P-P

8 spades and 6 or 7 playing tricks so some people may bid only 3♠ s. Then would West raise to 4♠ s. He has 3 tricks (2 Aces and 50% of 2 finesses), the J♦ and doubleton spade (one more than partner will have used to calculate his playing tricks) suggests raising to 4♠ s.

P - 1♣ - 1♥ - P

2♥  - P - 3♥ - P

4♥ 

North's hand has good shape though K♣ is probaly worthless, so probably 2♥ s is the maximum.

South is a maximum so can invite with 3♥ s which North can easily accept.

1NT - P - P - 2♥ 

P- P - 3♣  - P

In duplicate it is not normally good to let the opposition to play in 1NT so West has a reasonable 2♥  overcall. South not being NV is probably best to bid 3♣.

1♦ - P - P - x

2♣  - 2♠ - P - 4♠ 

Double by North allows the possibility to find a ♠  fit and keeps the option to bidding ♥ s later.

East has a choice of 2 or 3♣ , with the double of 1♦ has weakened the Q♠ doubleton, so probably 2♣ s is best.

South should show ♠ s as preference to the ♣ s and (if East passes south should jump to show 8+ HCPs).

The South "free bid" of 2♠ s show 8+ HCPs.

North has great shape and has to decide between inviting with 3♠ s and bidding 4♠ s. Difficult for 4♠ s is that you know most of the points will be in the East hand, 6 loser hand and a good source of tricks in ♥ s.

Those playing 3 weak 2s may open 2♦ s with west.

South may overcall East with 2♥  Michaels showing ♠ s and a minor (though many people play this bid as two highest unbid suits).

After the vulnerable 3♦  bid west can jump to 5♦ . The bid of 4♠ may show a good raise to 5♦ s and invite a slam and East may then bid 6♦ .

Some North's may bid 1♣ with the intention of re-bidding 2♣ , but with 5332 1NT is probably better.

East has the choice of bidding 2 or 3♠ , the hand has a waster Q♥ singleton, but the J♠ could be good and the K♣ sitting over the 1NT bid and it shows a 6+ lond ♠ suit.

West will raise 3 to 4♠  and with the 5 ♠ s opposite a minimum 5♠ s should bid to the level of the fit (law of total tricks) and raise 2 to 4♠ s.

The lead of 5♥ is the normal lead but unfortunately gives a trick away. 

East can bid 2NT as unusual showing ♥ s and  ♦ s . 

South could bid anything between 3, 4 and 5 ♣ s. Probably best to bid 3♣ at this vulnerability as they might not have a game on or bid it.

Likewise North may pass West's 3♥ s to see if they get to game.

When it comes around again to North he has the possibility of a risky 5♣ bid.

Then East or West have to decide whether to double or bid 5♥ s?

Not a good week for standard leads J♠ is a natural standard lead of top of internal sequence.