Maybe a little of both.

While God did not chastize them for having many wives, he also didn't stop the problems that came with that arrangement. Sin more often than not, punishes itself.

"Neither shall he multiply wives to himself, that his heart turn not away'

Solomon had to do A LOT of repenting because his heart was "turned away" due to his many wives.

He had 700 official wives and 300 concubines (and I wonder if those numbers are "rounded" of to the nearest 100)

Of Solomon the Inspired Record says, "His wives turned away his heart after other gods: and his heart was not perfect with the Lord his God." 1 Kings 11:4
" Solomon's course brought its sure penalty. His separation from God through communication with idolaters was his ruin. As he cast off his allegiance to God, he lost the mastery of himself. His moral efficiency was gone. His fine sensibilities became blunted, his conscience seared....Solomon turned to find satisfaction in the pleasures of sense"

And David -- had he been committed to being faithful to one wife instead of taking seven wives and at least ten concubines, would he have so readily fallen with Bathsheba? And then married her as his eighth wife.

"The bitter result of marrying many wives was sorely felt throughout all the life of David. {PP 668.1}

How many wives did Saul have?

Saul married Ahinoam, daughter of Ahimaaz. They had four sons and two daughters. The sons were Jonathan, Abinadab, Malchishua and Ish-bosheth. Their daughters were named Merab and Michal.

Saul also had one concubine named Rizpah, daughter of Aiah, who bore him two sons, Armoni and Mephibosheth

A comment by Jonathan Gallangher:

Two points mentioned in the lesson comment in Spectrum:

1) To David the goal is to alleviate the land of Israel from the famine. But instead of asking Yahweh how He wants that done, he asks the Gibeonites what they want.

2) The question that the story raises is obvious: if the death of Saul’s sons and grandsons was required for expiation of his guilt and Yahweh was awaiting their death to end the draught, why did the rains not come immediately?

I think the problem comes from taking the story out of its context in scripture.

When one reads the continuous story of David in 2 Sam. we see that there were considerable problems between the "house of Saul" and the "house of David".

God had said -- "David is My choice as king -- his throne is to last forever (and yes, Christ is in the line of David)(See 2 Sam. 7)

Saul's descendents said, "It's not fair, we want the kingdom restored to the "house of Saul".

You will see this in the stories preceding this account.

ABSALOM REBELLS DAVID IS FLEEING

Ahh --- David is now weak! What happens.

We see Ziba (servant of Jonathan's son Mephibosheth) come to help David. David asks him, "Where is your master, Methibosheth's son?"
NOTE THE ANSWER.
"he abideth at Jerusalem: for he said, To day shall the house of Israel restore me the kingdom of my father. 16:3

David disinherits Mephibosheth's Son Mica, and gives all the property to Ziba.

NOTE AS WELL,
While David is fleeing,Shimei, of the house of Saul is running along on the other side cursing, and throwing stones at them, shouting things like "The LORD hath returned upon thee all the blood of the house of Saul, in whose stead thou hast reigned;" 16:8

Of course when David is back in power Shimei comes pledding for forgiveness knowing full well his behavior could result in his death.

NOTE AGAIN:
As David returns to Jerusalem another rebellion breaks out.
"Sheba, the son of Bichri, a Benjamite: blew a trumpet, and said, We have no part in David, neither have we inheritance in the son of Jesse" 20:1

David figured Sheba would do more harm than Absolom. But David's men managed to quell the rebellion -- with the help of a wise woman.

BUT NOTE:
This story of Ripzah comes AFTER all these rebellions against David's throne.
The house of Saul was NOT willing to take God's choice as final, they wanted the kingdom back.

Micah, Saul's daughter, and one of David's wives, reveals a spirit of contempt and bitterness towards David. Was it only during the "ark" incident? Or was that incident a picture into her heart?
Scripture says the five grandsons that were hanged were brought up by Micah. Some think this is a mistake because Merub, Micah's sister was married to Ariel. However, Merub may well have died, and Mical raised up those five boys. Did she also help instill a spirit of rebellion in those five boys.

LASTLY NOTE:

After the stories of the rebellions, followed by the incident of Rizpah, and a few more battles, David sings a song.

"22:1 And David spake unto the LORD the words of this song in the day [that] the LORD had delivered him out of the hand of all his enemies, and out of the hand of Saul:
22:40 For thou hast girded me with strength to battle: them that rose up against me hast thou subdued under me. "


So my conclusion --
These young men didn't just die for Saul's sins,
they died for their own. Saul's descendents were not content to accept God's choice of king. They were a threat to David's throne and (judging from what happened when David was fleeing Absalom) were simply waiting for a point when David was weak or dying to stage a revolt.

Saul's killing of the Gibeonites and breaking the oath, was just another reason why the kingdom would not pass on to Saul's descendants.

Why did God wait 30 some years before rectifying this situation with the Gibeonites? Probably because Saul's sons and grandsons were given time to reveal their own characters.

God worked it out that they would no longer be a threat to the throne.

Why didn't it rain right away?
Because there was more that needed to be done. The burial and respect paid to the deceased finally brought peace between the house of Saul and the house of David.

But, as the lesson pointed out, "most Bible commentators agree that 2 Samuel 21–24 do not unfold sequentially after 2 Samuel 20 but rather they provide further information that does not fit into the general storyline of David’s life."


Is the non-acceptance of the authority of a king a sin punishable with death?
The fact is, God didn't require the life of anyone - the gibeonites did. And the death of the seven men didn't bring the rain - the reconciliation of the nation did.