Any “all scores” rule at colleges that have them do not include tests taken in 8th grade or before, but 9th grade is included.
As to sending official scores, you can do so for a single charge per college for all your SATs and subject tests but ACT charges a separate fee per test per college.
Stanford requires all ACTs and all SATs, but you can send whatever subject tests you want to send. As to your not wanting to send the SATs, that means you do not want to follow a requirement for admisison, which is not proper to do. When you submit both SAT and ACT to Stanford, it, like other colleges, will use to determine admisison that test it believes has the higher score. As to whether Stanford would find out you concealed your SAT scores, the answer is that it mainly depends on what your high school does. Many high schools put all your scores on your offical high school transcript sent to colleges, and thus, if yours does so, if you withhold sending scores through College Board, Stanford will learn you did so through your transcript.
Yale, by the way requires either all ACT scores, or, alternatively, all SAT and all subject test scores. If you send any subject test scores you must send all SAT and all subject test scores. It is also pointless to send ACT and subject tests without SAT scores. It views the ACT as a test separate for consideration from both the SAT and subject tests. Thus, if you submit ACT and subject tests, only the ACT will be used to determine admission; you must submit SAT for the subject tests to be considered.