Per part 142, you don't need an ATP, you just have to meet the requirements for an ATP. 142.47:
ii) If instructing in flight simulator or flight training device that represents an airplane requiring a type rating or if instructing in a curriculum leading to the issuance of an airline transport pilot certificate or an added rating to an airline transport pilot certificate, meets the aeronautical experience requirements of §61.159, §61.161, or §61.163 of this chapter, as applicable
No Instructor ratings required, the training center has to give training about training. Again, 142.47:
Prior to initial designation, each instructor shall:
(1) Complete at least 8 hours of ground training on the following subject matter:
(i) Instruction methods and techniques.
(ii) Training policies and procedures.
(iii) The fundamental principles of the learning process.
(iv) Instructor duties, privileges, responsibilities, and limitations.
(v) Proper operation of simulation controls and systems.
(vi) Proper operation of environmental control and warning or caution panels.
(vii) Limitations of simulation.
(viii) Minimum equipment requirements for each curriculum.
(ix) Revisions to the training courses.
(x) Cockpit resource management and crew coordination
There is no way to get a FAA PVT, COMM or ATP without holding a medical.