There are limited scholarships out there for families with multiple siblings attending college at the same time. However, these are generally geared toward families that have multiple siblings such as twins, triplets and quadruplets. While you may find one or two sibling scholarships out there, I suggest you research the colleges for which you are applying to see what they have to offer. You will find some colleges that do offer sibling scholarships, but not all of them do.
Many colleges and universities offer discounts to students who have siblings attending college at the same time in the same institution. In your research, doing a web search for "tuition discounts for siblings" will reveal several schools offering these discounts.
Some colleges, like the University of Hartford, have a family grant program. Like any grant, they have certain criteria or guidelines that must be met. When applying to a college, research the grants that they offer for incoming and current students. They may have one to suit your needs.
Don't forget to fill out your FAFSA (Free Application for Federal Student Aid) online at the FAFSA website. Through this site, you use your tax return to fill out the appropriate information required in applying for federal aid. You may be determined eligible for a Federal Pell Grant or your college may grant you a FSEOG (Federal Supplemental Education Opportunity Grant) depending on your income level and the number of individuals in your household attending school at the same time. They also offer loans based on the information provided to them.
There are many avenues to follow in finding college tuition assistance. One site you should search is the College Board, which is also the site that lists your SAT scores. They have a search application for scholarships, grants and loans. Fast Web is another site that is free to use in searching for tuition help.