I’m slightly confused about certain aspects of taqlid, so someone like Sayid Hakeem was considered a top marja right up there with Sistani, but he did have some differing opinions on laws (such as permanent marriage to ahlul kitab as well as removing care when someone is brain dead being permissible). My question is, if both are top scholars but they share differing opinions, why is it haram to accept something hakeem said, but if he had become the top marja it would’ve been okay?

It’s natural for scholars to disagree on some rulings. Remember, the Qur’an and hadith came over 1000 years ago. Scholars do extensive research to figure out what the Prophet and Imams said. Which hadith is authentic or not. Who are the narrators who narrated them? What does the hadith mean? What was its context? Naturally experts will disagree on some details, just like doctors disagree on some details.

Now if you follow Hakeem because you believe he is the most qualified, then you are justified in following his rulings. On the Day of Judgement you can say to Allay: he was the most learned expert in my view and I followed him to know what my Imams said. That’s legitimate. But let’s say there was a more learned scholar in your opinion, then what would be your justification for following Hakeem? Scholars are split here. Many say you have to follow the most learned while some say as long as you are following an expert then it’s acceptable. If you, between you and Allah and after researching this point, you believe you can follow multiple Marja’s even though one is more knowledgeable than the other, that’s fine you can do that. It’s not haram. However, make sure when you do so you are not shopping around for convenient fatwas—but that you a reasonable reason for doing so.