Getting into a BS/MD program is exceedingly difficult and requires, in part, stellar academics (eg very high grades and standard test scores), Acceptance into these programs is on par with Ivy League schools (<5%).
Understand that med school application process is a year long process meaning if you plan to go to med school after two years at a UC, you would need to submit a competitive application in the summer after your first year at a UC. This means that you would, in part, need a MCAT score. It would be best that you completed all premed reqs before taking MCAT which would be an interesting trick not only because as a premed you need 2 years of chem, you’ll need to pencil in perhaps two months prepping for MCAT. and don’t forget to pencil in 100 hours of time for ECs while at the UCs. ECs done in hs will be of little to no value to you on a med school application. Also, if offered, you would be required to attend interviews in your second UC year while trying to finish major reqs/graduate. And since most successful CA applicants attend med school OOS, you would have to find time to travel OOS.
In last cycle approx. 59% of those that applied failed to get even one acceptance to med school and that of those that got accepted, approx. half got an acceptance to only one med school. There’s a saying that getting into med school is a marathon, not a sprint. It’s best to apply one time with strongest possible application. I can understand the economics of graduating from college with as little debt as possible, but as to your UCs plan, what you’d really “like to do…” is not realistic. You need to rethink your 6 year plan UC plan. Good luck