You've already gotten great advice and support here, but I'll chime in anyway, just in case one more voice supporting what you did helps. Your dad's e-mail is ironic, because you are doing this because family is so important to you--you are taking steps to preserve the familial relationships, keep people on equal footing, and not let something like money come between you and your brother. Stay strong, and know that your parents are the ones who are prioritizing money over family right now.
Also, on an unrelated issue, I had a huge blowout with my parents when I was 30 (they didn't like how I was raising my toddler and tried to force my hand...literally, wanted me to spank him when that's something I was against). They "banished" us for a summer, wouldn't come to my house if he was there (Really? I'm going to send my two-year-old away so you can visit? I think not.). It was excruciating for me, because I'd never really broken away from them psychologically as I should have, never rebelled, and still sought their approval. If it had been any other thing besides my son, I probably would have caved, but I had a responsibility to him that outweighed my desire to be the dutiful daughter.
I was sick to my stomach over it for weeks, kept replaying conversations in my head, cried, talked about it obsessively with friends and colleagues, but stuck to my guns. It took a long time, but things are better than ever between us. I needed to break away in order to come back into the relationship as an adult--I should have done it much, much sooner! I've never gotten anything like an apology from my parents (they're not the sort, as they're never wrong), but my mom did say that I have really great kids, and that perhaps all those things I did when they were little didn't hurt them after all, and if anything, made them nicer. I appreciated her words, but the biggest point here is that I didn't need them. I can't tell you what a relief it is to have appropriate boundaries.