(a) Tokaido LineYes, between Tokyo and Atami.
Shonan-Shinjuku Line
Yes, along its entire length.
(c) Keihin-Tohoku Line
Yes, along its entire length.
I am confused because Tokaido & Shonan-Shinjuku Lines go from Ofuna toward Tokyo but what about from Ofuna towards Atami?
Westwards, the JR East network extends as far as Atami (plus down the east coast of the Izu Peninsula). So, you can take any local, rapid and limited express train along the Tokaido and Shonan Shinjuku Lines as far as Atami. But the Tokaido Shinkansen is not covered.