3 are simply different aspects of forms

These 3 are simply different aspects of forms. Each kaya has 3 different facets. For example, the

dharmakaya of dharmakaya is Buddha Samantabhadra; the
sambhogakaya of dharmakaya is Vajradhara; the
nirmanakayas of dharmakaya are the 5 lords of the buddha-families.

So, Amitabha, as head of the Lotus family, is classified here as nirmanakaya. The

dharmakaya of sambhogakaya is Vajradhara; the

sambhogakaya of sambhogakaya is Vairochana Gangchentso; the

nirmanakaya of sambhogakaya is Sakyamuni Buddha. The dharmakaya of nirmanakaya is Amitabha; the

sambhogakaya of nirmanakaya is Chenrezig; the

nirmanakaya of nirmanakaya is Guru Rinpoche.

So, here, Amitabha is the dharmakaya.