I can see having two different KGs (mother & father from different KG backgrounds).
Three? Seems like a long shot.
Problem is, only, like, 4 are actually KGs.
The others (assuming Fourth's clan justu ideas are put in) are just stuff you have to work on your entire life.
Right, but KG are also clans, right?
Kaguya clan. Uchiha clan. Hyuuga clan. etc.
The difference is that those clans, in addition to having secret jutsu, also have a bloodline limit that compliments their specific jutsu.
You could theoretically have 2 different bloodlines in one person that have enough presence to be usable, but regardless, you can only be in one clan.
Having the presence of two different KG could buy you membership into those two clans (so you could learn
those clan secrets) but it would not buy you admission into a non-KG clan to learn those jutsu.
Again, just my opinion.
I know that some want all, but let's keep it realistic and be thankful we have KG at all.