Yes, you recall correctly. Change of custodian on a non spouse inherited IRA can only be done by direct non reportable trustee transfer, but there is no limit on the number of these you can do. Be very careful to avoid requesting anything that could be construed as a distribution request, since a check made out to you will be fully taxable with no fix available for this.
Also, when consolidating to C be sure that all these accounts were inherited from the same decedent AND have the same RMD divisor. Finally, if inherited from the same decedent, your RMDs can be aggregated, although consolidating to one account would make that irrelevant.