I don't get the need for Marley to be in his own room, especially in light of his early lonely months when he couldn't see. If they think its going to help with his sleep, I think they might be in for a rude awakening - I admit that I moved my daughter into her own room just shy of 6 months (like 2 weeks, not 2 months like Joe!) but she'd stopped feeding in the night and was only disturbing because she was being woken by myself and my husband. But she was only a few feet away in her room, not on a separate floor of the house! Yet despite sleeping through the first few nights, teething hit hard and we had weeks of nightly wakings of screaming in pain, bringing her back in with us and so on, plus replacing the dummy countless times.
I know others who moved their babies earlier than 6 months BUT they don't have huge followings on a social media platform who are influenced by what they are doing. All the 'you dont need to justify it'. No, you don't need to justify it to yourself if that's the decision you've made. But you do have a responsibility if you are sharing parenting 'advice' that goes against what are guidelines.