As Mauro ALLEGRANZA notes an "atomic sentence is a proposition symbol". You cannot have more than one atomic sentence contained within an atomic sentence. That is why they are called "atomic".
However, more generally a sentence (not an atomic sentence) can contain multiple sentences (some of which may be atomic sentences) which are connected by logical operators. In the example provided, A ∧ B ∧ ¬C would be such a sentence containing the sentences A, B and ¬C separated by the conjunction logical operator. Even these are not all atomic sentences. ¬C contains the atomic sentence C with the negation operator.
One side issue is operator precedence. To not allow ambiguity in assigning a truth value to these sentences, parentheses are often used. According to the "Operator Precedence" chapter of Stanford's Introduction to Logic, one needs to identify rules for whether to write A ∧ B ∧ ¬C as (A ∧ B) ∧ ¬C or A ∧ (B ∧ ¬C).
Here is how that source describes this situation:
In unparenthesized sentences, it is often the case that an expression is flanked by operators, one on either side. In interpreting such sentences, the question is whether the expression associates with the operator on its left or the one on its right. We can use precedence to make this determination. In particular, we agree that an operand in such a situation always associates with the operator of higher precedence. When an operand is surrounded by operators of equal precedence, the operand associates to the right.
So in this case the association would be to the right. That is, if one wanted to avoid ambiguity one would write A ∧ B ∧ ¬C as A ∧ (B ∧ (¬C)).
"Operator Precedence" Introduction to Logic http://intrologic.stanford.edu/glossary/operator_precedence.html