Read the expressions in a loud voice.

Read the expressions in a soft voice.
Read the expressions loudly.
Read the expressions out loud.
Read the expressions aloud.
Read the expressions loud.
Read the expressions softly.
Read the expressions in a low voice.
Read the expressions softly.
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Are the expressions above all grammatical? Do we use them frequently?

All of your expressions are grammatical except for this one: "Read the expressions loud." Loud is an adjective, but the adverb loudly would be correct here.

William shared 8 apples equally among 4 friends

Yes, all of the expressions listed above are grammatically correct. They are commonly used variations for instructing someone on how to read aloud with different voice volumes or tones.

While the frequency of usage may vary depending on the context and individual preferences, these expressions are commonly used when giving instructions for reading aloud in different ways.