Take a look at :-
https://dnapainter.com/tools/sharedcmv4This website should be bookmarked by anyone using DNA.
For each relationship you can see the Mean Shared DNA & the Range of cM that their data has.
It is the Best website for checking on the likely DNA Relationships with a DNA Match.
Now with your:-
His sister No. 1: 22cM/2seg
Sister No. 2: 9cM/1seg
Brother No.1: 9cM/1seg
Brother No. 2: 17cM/1seg
If we enter 22 in the DNA Painter, which I suggest you do that yourself.
We get a far more distant relationship likelyhood than a 3C, there is only a 16% Probability of a Half 3C and 58% Probability for the more distant.
As Glen suggests, building wide and deep is a good foundation with DNA Research.
A possible hypothesis in this case is that the four Brothers are perhaps a Second Cousin with the person who you are seeking as the Father and hence going back much further and extrapolating wide may lead to possible Fathers being identified.
I too have a complicated family tree, and in the tree of a relation whose DNA I manage they have an unknown Great Great Grandfather, finding him is still a work in progress even after so many years. I do have one candidate who fulfils the means, motive and opportunity criteria seen in many a Police drama, the person lived in the next village at the same time as conception occurred, alas the “going wide” in this case found the man but the DNA Match is via his Uncles line and hence a very lowish cM shared with the match led to this tree build and so I have nothing to substantiate the hypothesis of him being the Father.
DNA can be a waiting game.