Wow! Congrats on the acceptances - you got in to some of my favorite schools! I'm just an future applicant, but I'll give my opinion.
Research: UCLA > UW = Northwestern.
This was based on your interests and descriptions of PIs. It can change according to your interests (eg genetics vs immunology). Fred Hutch is incredible if you want to go into cancer biology and Caltech is amazing if you want to do bioengineering. All the schools listed here have phenomenal research opportunities for bioengineering and cancer research, so pick the school where you see the best mentors.
Cost of Living: Northwestern > UW > UCLA.
Seattle is quickly becoming one of the most expensive cities to live in due to Microsoft and Amazon raking in all the CS people. The low stipend is something that their grad students frequently protest. However, LA's cost of living is outrageous. Owning a car in LA will cost fortunes, not to mention the traffic. Northwestern would probably be the most friendly for owning a car and building up some savings.
Vibes with students and staff: UCLA > Northwestern > UW.
This is subjective based on what you described. Given your acceptances to these programs, you should probably reach out to current students to discuss life at these schools in a less formal setting. That would probably clear things up with Northwestern and UW. Maybe try to reach out to some other accepted students. If you don't vibe with your colleagues/mentors, 8 years is not gonna be fun.
Family: Its sounds like your family is closest to Northwestern??? Depending on your goals, this could play a factor in moving to the WEST SIIIIDE.
Extracurricular activities: depends on your interests. Food, outdoor stuff, museums... The west coast is beautiful with tons of outdoor activities, making it great for people who like to explore nature. Chicago can get brutally cold, but if you're a foodie or museum junkie, it can be really fun too.
I'm not sure how you're ranking things, but given the importance of research and quality of life, it sounds like you'd be a great fit for UCLA. This is just my opinion. Again, huge congrats on those A's!