There are several choices with what to do with Miranda: 1) Let him work through it as the regular third baseman. 2) Reduce his workload by using Farmer as the alternate 3b, play him some at first and DH. 3) Option him to the minors or 4) place him on the Injured List, if there is still some problem with his right shoulder.
Right now, playing Miranda essentially every day isn't working and the replacements give us no reason to be optimistic for an offensive surge. Kyle Farmer is a decent defender and very good against left handed pitching. Willi Castro is a utility player, with a lifetime 87 OPS+. Because of this, I think you keep Miranda on the team, for now, unless he is bothered by an injury. If there is an injury concern, I would hope the Twins give him ample time to heal up and then rehab to find his stroke.
Miranda seems to be pressing mightily. He is jumping at pitches early in the count and making a lot of weak contact. He's not hitting line drives much and hitting plenty of grounders, leading to a lot of double plays. He has been poor in the field, both handling grounders and throwing. It is time for some sort of reset. If there was a better option in the wings, it could be a demotion, but I think he might lose some playing time and get some first base time. If I'm GM, I DFA Donovan Solano tomorrow.