the idea for the fearless is to be optimal with only around 10-15 ppl. - mainly due to the fact that it is essentially not a warship - but an armored transport. in its usual state it does not require rotating shifts or high alert levels - so the crew is mainly a small bridgecrew, some gunners and cargo workers.
no idea about the BC, but around 100 seems right depending on the alert level and deployment - so yea - 50-100.