I get plenty of hot water to both showers, but can't get any in either bathroom sink, and only a trickle to the washer.
The faucets are both new single handle type, and the plumbing is new to the washer. What could be causing this ?
Did the plumber fail to open the valves on the supply lines after the installation?
"but can't get any in either bathroom sink, and only a trickle to the washer. "
By "any" do you mean any water at all or any hot water in the sinks?
On the washing machine - there may have been some debris in the Hot water line which could be clogging the washer inlet. Assuming the valve is fully open you may want to close it and disconnect the line from the rear of the washer. The washer inlet usually has a small screen in place and it could be blocked and just needs cleaning.
Best guess with limited info.
Under the sinks, detach the hot water line and use the angle stop valves to run a bit of water and see if you're getting hot there. If so, then the faucets were somehow installed incorrectly so that they are not delivering any hot in any position. The single handle types have some complex innards that the installer may not have been familiar with.
Another possibility is that the plumber hooked the a new hot water supply line to some existing red PEX, assuming it was a hot water line [as it should be[, but it was in fact a cold water line, which should be blue PEX.
On the faucets, be sure the aerator is clean. The instructions note to remove the aerator and run the water to flush debris before replacing it.