In the case of multiple persons, would balance be plural?

Solution 1:

When the word is reckoned with as having at most a unique referent for each individual it is usual to keep the word in the singuar. This can be verified for the following words and others.

• interest, understanding, hatred, love

However, when the word can be reckoned with as having more than one referent for each individual, then the plural tends to be more frequent, this, along the line of a gradient according to the greater plausibility of more than one referent. In the case where several referents are involved for each person the plural must be used. It is not clear whether the plural might not be used also sometimes when there is a unique referent.

Solution 2:

This is an excellent question that raises an issue that seems backward. When deciding numerical agreement, you always match singular with singular, and plural with plural. Here, "us all" refers to a GROUP, so it SEEMS plural. But it is not. It is ONE group, not many. So the referent must be singular: "I lose my balance. The group loses its balance." If it were truly plural, it would be referring to separate items: The balances of bass, treble, and midrange required adjustment.