We measure electron- and nuclear-spin transition frequencies in the ground state of nitrogen-vacancy (N-
V
) centers in diamond for two nitrogen isotopes (
14
N-
V
and
15
N-
V
) over temperatures ranging from 77 to 400 K. Measurements are performed using Ramsey interferometry and direct optical readout of the nuclear and electron spins. We extract coupling parameters
Q
(for
14
N-
V
),
D
,
A
‖
,
A
⊥
, and
, and their temperature dependences for both isotopes. The temperature dependences of the nuclear-spin transitions within the
0
spin manifold near room temperature are found to be 0.52(1) ppm/K for
14
N-
V
(|
m
I
= −1⟩ ↔ |
m
I
= +1⟩) and −1.1(1) ppm/K for
15
N-
V
(|
m
I
= −1/2⟩ ↔ |
m
I
= +1/2⟩). An isotopic shift in the zero-field splitting parameter
D
between
14
N-
V
and
15
N-
V
is measured to be ~ 120 kHz. Residual transverse magnetic fields are observed to shift the nuclear-spin transition frequencies, especially for
15
N-
V
. We have precisely determined the set of parameters relevant for the development of nuclear-spin-based diamond quantum sensors with greatly reduced sensitivity to environmental factors.