Some Sharkbite fittings will connect copper to PEX. Pricey though.
In my case the female fittings on the end of the PEX tubes screwed right onto the male fittings on the ends of the copper faucet supply lines.
I replaced our kitchen faucet with a Moen with pull out sprayer wand. I had to use a hole saw on the plastic sink where the supply tubes go to make room for the sprayer hose, but other than that it was a drop in replacement.
The bathroom faucet was a drop in replacement but as others have said it was easier to remove the sink. Space is really limited under the sink on mine.
Clay (WA5NMR), Lee (Wife), Katie & Kelli (cats) Salli (dog).
Fixed domicile after 1 year of snowbirding and eleven years Full Timing in a 2004 Winnebago Sightseer 35N, Workhorse chassis, Honda Accord toad