I think KJ can. 2-way contracts are open to players in their 4th NBA season or earlier. KJ's only played 3 years and so has Goodwin. You're right on Jenkins.
Not according to the CBA: “ (f) Eligibility. The following eligibility rules shall apply to all Two- Way Contracts: (i) No Team may sign a player to a Two-Way Contract after January 15 of any Season. (ii) No Team may sign or convert a player to a Two-Way Contract if the player has or may have four (4) or more Years of Service at any point during the Contract. For example, a player with three (3) Years of Service would not be eligible to sign a Two-Way Contract with a term of two (2) years. (iii) No Team may sign or convert a player to a Two-Way Contract, or acquire a Two-Way Contract by means of assignment, if, as a result, the player would or could be under a Two-Way Contract for any part of more than three (3) Salary Cap Years with the same NBA Team. For example, a player who completes a two-year Two-Way Contract with a Team could not subsequently sign a two- year Two-Way Contract with that Team.” So guys with three years of service can be signed to a 2-way contract, but only for one season.