Could Vegeta, Piccolo or Tien learn kaioken?

[Warmmedown]

Is there any prerequisite to safely learn kaioken, such as to have a calm demeanour?

Could Piccolo push kaioken further by healing in between?

 

[SSJ2]

I could see Vegeta being able to do it being a Saiyan and being able to pick up Ki related techniques easily. Piccolo probably could have. He was a direct rival to Goku when Goku arrived on Kaio's planet and was basically his equal. I don't think his healing would influence his usage of Kaioken given that it merely regenerates limbs.

I highly doubt Tenshinhan could learn it given he was on Kaio's planet for so long and never used the technique. It's possible he learned how to infuse it into his Kikoho to create the Shin Kikoho - which was powerful enough to hold down Semi Perfect Cell. That's not possible without an outrageous amplification.

 

[Spiral-Force]

They should be able to. Main thing to consider upon use is the body potentially destroying itself when sustained beyond what you're accustomed to. This very well could be a risk they would knowingly take because -- like Goku -- they try to max out all resources when the opponent is that fearsome.