Am I splitting my rent unfairly?

I live with 2 other roommates. I am the lease-holder and have been in my apartment for 5 years. Both other roommates have been here for less than 2. I pay the original amount of rent I have always paid, which is much less than they do (as I have been here for a few rent increases). They agreed to the amount of their monthly rent when they moved in and it won’t change while they are still living with me. We live in a very expensive city and their rate is well within current rental rates. One roommate recently found out that I pay less and is very, very angry. Can I get some feedback on the right thing to do? Am I being unreasonable?