Your Committee recommends that its quorum be fixed at seven (7) members, provided that both Houses are represented whenever a vote, resolution or other decision is taken, and that the Joint Chairmen be authorized to hold meetings to receive evidence and authorize the printing thereof so long as four (4) members are present, provided that both Houses are represented; and, that the Committee have the power to engage the services of such expert staff, and such stenographic and clerical staff as may be required.
they won't vote if only a single house is present.
They said both houses need to be represented if there is no be a vote, so my statement that they won't vote with only one house present is true according to the passage. 
( z1 vote :polarity - :ARG0 ( z2 they ) :condition ( z3 present :ARG1 ( z4 house :ARG1-of ( z5 single ) :mod ( z6 only ) ) ) )