Open-collector outputs, especially with 15 V tolerance, are unusual.
You'd have to combine an active-high decoder like the SN74AHC238 (or any other '238) with drivers like the TPL7407LA (with only 7 channels) or transistors.
No; 1:8 muxes are intended for signals with much less than 10 A.
Use a 3-to-8 demultiplexer with active-high outputs (e.g., SN74HCS238, SN74AHC238) for the control signals, and combine it with eight high-side switches (e.g., TPS27SA08).
