Double rex and hairless are separate genes, please do not refer to them interchangeably.
Hairless (a recessive) is associated with some visual females having milk issues, problems can be avoided by breeding carrier females to visual males. These are not among the rats OP has.
Rex and double rex (aka drex) are generally not an issue for feeders or breeding and have no milk issues as a general rule. (Any individual rat of any genetics could potentially have milk issues, but it would not be rex causing it in this case)
Drex and hairless do both result in rats with little to no hair, but the genetics behind it do make a big difference for the issues you bring up.
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