We report improved measurements of the product branching fractions B(B+ --> (D) over bar D-0(s0)*(+)(2317)) x B(D-s0*(+)(2317) --> D-s(+) pi(0)) (8.0(-1.2)(+1.3) +/- 1.1 +/- 0.4) x 10(-4) and B(B-0 --> D-Ds0*(+)(2317)) x B(D-s0*(+)(2317)) --> D-s(+) pi(0)) = (10.2(-1.2)(+1.3) +/- 1.0 +/- 0.4) x 10(-4) where the first errors are statistical, the second are systematic and the third are from D and D-s(+) branching fractions. In addition, we report negative results from a search for hypothesized neutral (z(0)) and doubly charged (z(++)) isospin partners of the D-s0*(+)(2317) and provide upper limits on the product branching fractions B(B-0 --> D(0)z(0)) x B(z(0) --> D-s(+)pi(-)) and B(B+ --> D(0)z(++) ) x B(z(++) --> D-s(+)pi(+)) that are more than an order of magnitude smaller than theoretical expectations for the hypotheses that the D-s0(*+)(2317) is a member of an isospin triplet. The analysis uses a 711 fb(-1) data sample containing 772 million B (B) over bar -meson pairs collected at the Upsilon(4S) resonance in the Belle detector at the KEKB collider.