how to change 12V in to multi out (9v, 5v, 12v)
You didn't give us the all-important information of how much current you need at each voltage.

For the 5 V a buck converter is most likely the best answer.  A linear regulator would dissipate 7 V times the current.  That's only 140 mA output to cause a watt of dissipation.

For the 9 V output you have less of a voltage drop, so a linear regulator might be OK.  It takes 330 mA output to cause a watt of dissipation.  If you need 150 mA or less, then a 7809 in free air would do, and would be 75% efficient.  However, unless you know the 9 V current is low, I'd go with a switcher here too.

At this voltage, there are many off the shelf switcher chips out there.  You supply a few external components, like inductor and input and output caps, hook them up like the datasheets says, and they work.  If you think this is beyond you or don't want to bother, just buy two off the shelf DC to DC converters.  They will cost significantly more than buck chips with the parts around them, but are really easy to use and just work.  For a one-off, the few extra $ may be irrelevant.