It's more about authenticity before the understanding. I will mention the 12 caliphs hadith later as it's the only Sahih hadith you've mentioned.
The first report =
أَخْبَرَنَا أَبُو يَعْلَى، حَدَّثَنَا عَلِيُّ بْنُ الْجَعْدِ الْجَوْهَرِيُّ، أَخْبَرَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ سَعِيدِ بْنِ جُمْهَانَ، عَنْ سَفِينَةَ، قَالَ: سَمِعْتُ رَسُولَ اللَّهِ
الخلافة بعدي ثلاثون سنة ثم تكون ملكا
The khilafah after me is thirty years, then there will be biting
Comes in different wordings from Safinah regarding the same topic. The other wording has two different chains =
حَدَّثَنَا عَمْرُو بْنُ عَوْنٍ، حَدَّثَنَا هُشَيْمٌ، عَنِ الْعَوَّامِ بْنِ حَوْشَبٍ، عَنْ سَعِيدِ بْنِ جُمْهَانَ، عَنْ سَفِينَةَ، قَالَ قَالَ رَسُولُ اللَّهِ
حَدَّثَنَا سَوَّارُ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا عَبْدُ الْوَارِثِ بْنُ سَعِيدٍ، عَنْ سَعِيدِ بْنِ جُمْهَانَ، عَنْ سَفِينَةَ، قَالَ قَالَ رَسُولُ اللَّهِ
خِلاَفَةُ النُّبُوَّةِ ثَلاَثُونَ سَنَةً ثُمَّ يُؤْتِي اللَّهُ الْمُلْكَ مَنْ يَشَاءُ - أَوْ مُلْكَهُ مَنْ يَشَاءُ
The Prophetic khilafah will last for thirty years. Then Allah will
give the dominion to whomever He wills.
Both are in (Sunan Abu Dawud)
And a similar one from Abu Bakrah =
حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا حَمَّادٌ، عَنْ عَلِيِّ بْنِ زَيْدٍ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ أَبِي بَكْرَةَ، عَنْ أَبِيهِ، أَنَّ النَّبِيَّ
خِلاَفَةُ نُبُوَّةٍ ثُمَّ يُؤْتِي اللَّهُ الْمُلْكَ مَنْ يَشَاءُ
There will be a caliphate on the model of prophecy, then Allah will
give the kingdom to whom he wills.
(Sunan Abu Dawud)
All four of these ahadith have weakness in them.
First, second and third isnad contain سَعِيدِ بْنِ جُمْهَانَ who has been weakened by some scholars due to him making occasional mistakes as Imams Nasai and Abu Dawud mentioned. But over all he's alright.
However the main issue is with the Sahabi named Safinah. He narrated these reports when he was old and he was not in the right state of mind. His potential had been harmed from problems due to his age. So the ahadith he reports aren't taken as strong nor accurate.
The hadith from Abu Bakrah comes through عَلِيِّ بْنِ زَيْدٍ and he's been abandoned or at least declared to be a unreliable narrator.
The last hadith you've mentioned, the narrators are =
حَدَّثَنَا سُلَيْمَانُ بْنُ دَاوُدَ الطَّيَالِسِيُّ، حَدَّثَنِي
دَاوُدُ بْنُ إِبْرَاهِيمَ الْوَاسِطِيُّ، حَدَّثَنِي حَبِيبُ بْنُ
سَالِمٍ، عَنِ النُّعْمَانِ بْنِ بَشِيرٍ، قَالَ: كُنَّا قُعُودًا فِي
الْمَسْجِدِ مَعَ رَسُولِ اللَّهِ K وَكَانَ بَشِيرٌ رَجُلًا يَكُفُّ
حَدِيثَهُ، فَجَاءَ أَبُو ثَعْلَبَةَ الْخُشَنِيُّ، فَقَالَ: يَا بَشِيرُ
بْنَ سَعْدٍ، أَتَحْفَظُ حَدِيثَ رَسُولِ اللَّهِ K فِي الْأُمَرَاءِ؟
فَقَالَ حُذَيْفَةُ: أَنَا أَحْفَظُ خُطْبَتَهُ، فَجَلَسَ أَبُو
ثَعْلَبَةَ، فَقَالَ حُذَيْفَةُ: قَالَ رَسُولُ اللَّهِ
The Prophethood will remain amongst you for as long as Allah wills it
to be. Then Allah will raise it when He wills to raise it. Then there
will be the khilafah upon the Prophetic methodology. And it will last
for as long as Allah wills it to last. Then Allah will raise it when
He wills to raise it. Then there will be biting kingship, and it will
remain for as long as Allah wills it to remain. Then Allah will raise
it when He wills to raise it. Then there will be tyrannical (forceful)
kingship and it will remain for as long as Allah wills it to remain.
Then He will raise it when He wills to raise it. Then there will be a
khilafah upon the Prophetic methodology. Then he (the Prophet) was
First problem is داود بن إبراهيم الواسطي. No one said he was reliable except at-Tayalisi, but at-Tayalisi himself wasn't a strong critic. So the narrator Dawud remain unknown and his condition isn't clear (majhul al-hal),
Second issue is حبيب بن سالم. Abu Jafar al-Aqili mentioned him in his "Ad-da'afa al-Kabir'. And in the book 'at-Taqrib' he is said to be alright but makes occasional mistakes.
Therefore, this hadith is also weak unless proven otherwise.
The ahadith about the 12 caliphs are authentic and reliable. And one of these ahadith makes a reference of the Khilafah consisting of 12 caliphs =
Jabir b. Samura who said: I joined the company of the Prophet with my
father and I heard him say: This matter will not end until there
have been twelve Caliphs among them. The narrator said: Then he said
something that I could not hear. I said to my father: What did he say?
He said: He has said: All of them will be from the Quraish.
From this hadith, and several similar ones, I personally believe that the Khilafah ended with the 12th caliph, who was Umar bin Abdul Aziz. The succession from the Prophet had ended with Umar bin Abdul Aziz and the rest of the rulership, even up until today, was all corrupt one way or another. But this is my belief from the hadith and everyone is free to critic or agree, no problem, yet, it must be based on authentic evidence.