I wouldn't want to try to use a 3/8" line to feed two DW and a sink...while the DW probably have a float or level control and might just fill slower (and extend the wash cycle time), if one or both of them were on and you wanted to use the sink, the flows would be pretty pathetic. FWIW, the copper institute's recommendation for maximum velocity of hot water in a pipe is 5fps, and a 1/2" pipe would equate to 4gpm. Because of the squared factor of the area, dropping to 3/8" would end up about half of that. A kitchen faucet is flow restricted, and just about maxes out a 3/8" line on hot...throw in two DW, and it won't work well. I'd want to feed things with a 3/4" line, then tee off to the three devices using smaller pipe/hoses.