Is it permissible for someone to follow multiple marjaas at the same time? Can someone have more than one marja? If so, what if those two marjas have contradicting rulings on a certain matter. Let’s say one marja forbids tattoos abd the other one allows them, who do you follow in this case?

It is obligatory to refer to the most knowledgeable mujtahid in taqlid, except in issues on which he does not have a fatwa, where you can refer to the next in the knowledge.