Can you get it from a toilet? :O?

I live with my sister & her boyfriend. They both recently found out they have 'the clap' ... chlamydia ... We have two different bathrooms the main one & the one upstairs. I really offended them when I asked them to no longer use the upstairs one. That I don't want to share one, as long as they have the STI. Isn't it possible to contract it from a toilet or am I being the insensitive douche that they claim I am?... & if we have been sharing the main bathroom for a few days, before they found out, am I at risk? :O :/ Should I get checked?