This is what makes state and estar look so different: they are essentially the same word, apart from that e on the front. English words beginning st-, sp- or s plus a consonant pick up an extra e in Spanish.
st- / sp- → est- / esp-
Ser is the to be of characteristics, and it is more irregular than estar. You already had es and son without knowing where they came from.
You can reach somos by working backwards from son: drop the consonant that marks they and add the we ending.
Eres is the strangest of them. Relate it to es if it helps: es, eres.
Yo soy · Él es · Ella es · Ellos son · Ustedes son · Nosotros somos · Nosotras somos · Tú eres · Soy estudiante
In the whole Spanish language, just four verbs end the "I" form in -oy instead of -o.
Ustedes is the plural of usted, but it stops sounding formal once it goes plural. Everywhere in the Spanish-speaking world except some parts of Spain, this is simply how you say you guys.
Ustedes son
The clearest practical test of the whole distinction, in two questions that differ by one verb.
Ser on its own means being. Un ser humano is a human being, where humano is an adjective, so it comes after the noun. The same word can be a noun instead.
Es posible