You do have to be careful. Just b/c buns are litter mates or appear to be bonded in a stressful situation (like in a rescue with many other animals), this does not necessarily mean they have a firm bond. We had another member (Sharper) have an awful experience when she adopted two buns that were apparently bonded and they ended up having bad fights at her home, one bun required two ER vet visits. It’s not uncommon for there to be a bun who is clearly dominant, but the submissive bun may at some point try to assert his/her dominance over the other and that can cause scuffles.
If they are both altered and firmly bonded, they should be able to live together with few issues. Some pairs require two litterboxes, some require two food dishes, etc. Sometimes a larger condo or xpen helps them relax, each can have their own space. Every pair is going to be unique.
Are you thinking of adopting them?