coldtits, I have very similar issues with my 2 girls.
dd1 is a passive girl. placid, content (constant and pestering, yes, but never physical - other than constant touching)
dd2 is loud. always has been (and it seems so much worse because she is a petite little thing - looks like a china doll)
dd1 is noise sensitive, and cannot bear her sister to be distressed in any way.
so, tantrums over cleaning teeth means dd1 turns into a shrieking harpy too, as she is so upset that her sister is upset. it's like bedlam, tbh.
dd2 has also learnt that she gets whatever she wants if she is loud - so, whether she is exercising control over breaking routines, wants a toy that dd1 has, doesn't want to eat ehr meal - she just makes a noise in the hope that dd1 will be so distressed that I will call a halt ot it.
it is very hard ot mange - you have my sympathies - as dd1 genuinely believes that it is the end of the world for dd2, whereas dd2 is just making noise...
slowly, slowly it has got better. we worked a lot on getting dd1 to identify emotions. we hae reached the point, where, on a good day, she can dispassionatley look at a tantrumming screaming dd2, turn to me and say "dd2 is cross". she still needs physical reassurance form me that dd2 is ok - lots of stroking and hugs, but she no longer gets distressed herself.