How is it possible to adopt a fatwa when there are multiple opinions regarding it, and is it permissible to follow all four schools of thought?

A Muslim's duty regarding a difference of opinion is to prioritize what appears to him to be supported by evidence, if he is capable of independent reasoning and preferring one opinion over another. However, if he is a follower (muqallid), he should follow the scholar he trusts among the people of knowledge, and his responsibility is then fulfilled. If scholars differ, he should follow the one he deems most trustworthy. If they are equal in trustworthiness, some say he may choose, others say he should follow the easier opinion (which Sheikh Ibn Uthaymeen preferred), and yet others say he should follow the stricter opinion because it is more cautious.