If the committee agred to the substitution for the whole year, then it probably is as you outlined and B has two votes.
If a super-majority of owners is concerned about this, then you can hold an EGM and pass a special resolution to remove either or both of these members from the commitee.
Otherwise, you can propose a motion to the committee that it rescinds the substitution as it was a cynical and deliberate ploy to give one owner two votes on the committee. The absentee committee member muct have known they were going on holiday for a year so this is very much dirty pool.
Even if the committee doesn’t rescind the substitution, at least your objection will be on the record.