About many of them we just don't know a single thing, but there's enough material to say that at least those four are strong and often underrated...
(East) Kaioshin: he is actually weak as a Kaioshin, that's stated in many situations, that doesn't mean he is not relatively strong.
He is far stronger than Piccolo as stated... That means Piccolo + Kami + RoSaT training + pre-Tenkaichi training...
I would list that Piccolo at at least equal to 2nd stage Cell and at best as Ascended Super Vegeta... We don't know for sure... Anyway, I red the whole first part of Buu's saga and it seems that the power of Saiyans Kaioshin admires as far superior to himself, is "the power beyond Super Saiyan", that is what Goku will call Super Saiyan 2 further on.
That's again Super Saiyan 2 that makes Goku, Vegeta and even Gohan not worried too much about Darbula himself, while Kaioshin is.
Basically it's Cell Games scenario, beside the fact that there are three Super Saiyan 2s and so Cell/Darbula wouldn't be a threat at all...
Kaioshin is then something like a Super Saiyan Full Power... Maybe low on the scale, but still...
He could be like Cell Games Goku or like Buu's saga Gohan... Maybe a bit below... But remember how Cell Games Goku HALF power scared Vegeta that was able to turn 2nd and 3rd grade... I think Kaioshin is AT LEAST like that... Like half Cell Games Goku, or even more...
Majin Vegeta SSJ2 said to Goku that Kaioshin should have been stronger than them, but now they are stronger... It's mostly refered to SSJ2 to me... As SSJ1 I don't think they're much different from Kaioshin that was totally unaware of SSJ2, because he said he would have used another strategy if he would have know that there was something beyond SSJ1...
South Kaioshin: he is stronger than North and West that are stronger than East... We don't know much, but I often ask myself why Kid Buu, one in SSJ3 tier, would have had to absorb him in the first place... Maybe he was not that weak... Or Buu is used to absorb the second strongest to fight the strongest? Like he did with Gotenks and Gohan...
South Kaioshin could have been quite powerful, but it leads to the following...
Dai Kaioshin: here comes the uncommon notice...

He may be actually far stronger than South Kaioshin... Don't be fooled... South Kaioshin is stated to be the strongest AMONG THE 4 KAIOSHINS...
Dai Kaioshin is another league... It would be like comparing the 4 Kaios with Dai Kaio...
Dai Kaioshin could have had a power level way above that of South Kaioshin, he was the absolute God of the whole universe...
We know that by the time Majin Buu absorbed Dai Kaioshin he dropped down in power because of Dai Kaioshin gentle and naive nature... It doesn't mean he wasn't strong... Or the strongest, actually...
Dai Kaioshin could have been easily SSJ3 tier and Kid Buu could have absorbed South Kaioshin because cornered by either the two...
Actually, the power gap there is between Kid Buu and Super Buu/Buff Buu could be made by, if not also South Kaioshin, at least Dai Kaioshin...
I know.........
The Z-Sword argument...
But the manga never said that EVERY Kaioshin tried to pull the sword...
Even less that Dai Kaioshin ever thought to try at all...
Many confuses Dai Kaioshin with a normal Kaioshin, while he absolutely isn't...
Furthermore, the Z-Sword has been there for many generations before the one South Kaioshin and his brothers were born... Kibith referring as "many Kaioshin tried" could be totally unrealated to the 4 Kaioshins of the last generation...
We are talking of aeons of time, not just the last few millennia when the whole Majin Buu mess occurred...
And last but not least...
Kibitoshin: he is terribly underrated... For two main reasons... He is a Potara Fusion... Weren't they made of Character 1 X Character 2 multiplication?
The second reason is that as soon as he is born, he wanted to help Goku against SUPER BUUTENKS!!! Elder Kaioshin of course said he was a moron to think to be able to do something against THAT Majin Buu that was beating up Ultimate Gohan...
But wasn't him saying more or less the same thing to Goku a minute before?
Does it mean that Kibitoshin is SSJ3 tier? Not necessarily, but it can't be excluded at all...
I know that in this case Kibitoshin would have fought Kid Buu when SSJ3 Goku ran out of energy... But that final battle is forced... No one tries to use the best solution... Just like they didn't teleport Gohan to give AT LEAST a HUGE hand when they could, I don't see why Kibitoshin, stronger than any Earth destrution survived Z-Fighter beside maybe SSJ3 Goku, should have given an hand before...
The whole Kaioshin argument is complex... But I feel they are often greatly underrated compared to what instead they *could* be as power...