From your perspective, the #1 thing is to look at the financial planning aspect: what can you afford, and what do the net price calculators of various possible colleges of interest say?
For now, the kids should try to do the best they can in school. http://talk.qa.collegeconfidential.com/college-admissions/1995563-faq-high-school-college-prep-base-curriculum.html has some information on choosing high school courses for college prep purposes.
11th grade will be the standardized testing year. The PSAT in 11th grade is the one that counts for National Merit qualification (many colleges give big scholarships for National Merit status). Additionally, taking one each of SAT and ACT during 11th grade allows for chances to retake the initially higher one later if desired. The last SAT test date in 11th grade is often used for SAT subject tests by students interested in colleges that want them.