My husband and I wanted to move to California with my sister, but we're both in our late twenties. Can my sister sponsor us, or does it depend where we're coming from? Would it help if we found jobs here beforehand? Any estimates on how long we would need to wait?
You will need to get to know the Visa Bulletin:
http://travel.state.gov/visa/bulletin/bulletin_1360.html
A USC who is 21 or older may file an I-130 for a sibling on form I-130 found at
www.uscis.gov
The siblings must share at least one common parent (biological, step or adoptive relationships all count). The various relationships are defined in the Immigration and Nationality Act (INA). Parent and child are defined. If you have the same mother then it's easier.
The category is FB-4 (Family based-4th preference). When the I-130 is properly filed that will establish the "priority date" (PD). The PD needs to become "current" on the Visa Bulletin in order to apply for an Immigrant Visa (IV). The waiting time for FB-4 ranges from 9 to 22 years for an IV to become available, then there is additional time to process the application(s) and gather the required evidence (Police Clearance Letters and medical exams and vaccinations).
The FB-4 category means that your USC sibling files for YOU as the primary beneficiary and when the IV becomes available, your spouse and unmarried child(ren), under 21 y/o can come with you. YOU must qualify for a visa in order for your derivative beneficiary family members to get visas. Each of them must qualify for a visa and be "admissible" to the U.S. under the law as it exists at the time.
You may have difficulty entering the U.S. as a tourist because of the presumed "immigrant intent" because of an immigrant petition having been filed for you. In the early part of the waiting period it should be possible to visit BUT as the PD gets closer to becoming current entry will become increasingly difficult.
If you don't have B-1/B-2 visas yet, you may want to get them before the I-130 is filed. The visa is placed in your passport and is issued for 10 years to adults and 5 years for kids. You still have to be "admissible" at each and every entry into the U.S. You have to show strong ties to your home country to get tourist visas and overcome the presumption of immigrant intent. That doesn't mean you can't have a far off, distant immigrant intent, just at the time of the application for the visa and upon entries made on that visa. Eventually, you show up with an IV instead when you actually move here.
IF you and/or your spouse have the required qualifications to obtain an employment based nonimmigrant visa, certain categories have a "dual intent" which means that the I-130 will not be a problem. These are the H1-B "specialty occupation" workers and L-1 "Intra-Company Transferees". If Canadian or Mexican TN is another possibility. depending on qualifications, other possibilities may be available.
If you can get an employer to sponsor you for an immigrant visa based on a job offer, the employer files a Labor Cert with the Department of Labor and IF that is approved then has to file an I-140 with USCIS. Depending on type of job and what category it falls into the waiting times could be comparable to the FB-4, it varies by country and EB category. Read through the Visa Bulletin about the waiting times and read up on the job categories on the USCIS website (immigrant and nonimmigrant categories).
Good Luck,