Both combination shot scenarios you've described above are legal shots according to the World Pool-Billiard Association 8 Ball rules.
The rules for combination shots in 8 ball are much simpler than folks make them out to be sometimes.
- Players must always ensure that the cue ball first contacts a ball from the their own group. The 8 ball isn't part of either group (solids, stripes).
- Contacting a ball from the wrong group first results in a "standard foul".
- A "standard foul" results in the opponent taking ball in hand, anywhere on the table.
You're good in both scenarios as you hit your own object ball first with the cue ball.
Here are the relevant WPA rules which relate to this scenario (emphasis ours):
3.9 Standard Fouls (8 Ball)
If the shooter commits a foul, play passes to his opponent. The cue ball is in hand, and the incoming player may place it anywhere on the playing surface. (See 1.5 Cue Ball in Hand.)
The following are standard fouls at eight ball:
- (6.2) Wrong Ball First - The first ball contacted by the cue ball on each shot must belong to the shooter’s group, except when the table is open. (See 3.4 Open Table / Choosing Groups).
The "wrong ball first" foul is further explained in section 6.2:
6.2 Wrong Ball First
In those games which require the first object ball struck to be a particular ball or one of a group of balls, it is a foul for the cue ball to first contact any other ball.
Based on this, both of your scenarios are legal shots, and if you pocket one of your object balls, then you remain at the table. If you fail to pocket one of your object balls, then your inning is over and your opponent's turn begins. No foul is assessed.
Note that some informal rules state that kiss shots "don't count", so if that's the case, then the first scenario is a kiss shot and results in a foul. If this happens, it would either be ball-in-hand, or, the incoming player shoots from where the cue ball rests (depending again on the house or league rules your're playing by).
But regardless of the rules, the three-ball combination in your second scenario should be a clean shot no matter what, as you hit your object ball first and the ball pocketed is yours.