It's time and patience, as you probably know
I sometimes think they don't get fully comfortable with you till they're a year old and more laid back!
I've had a robo before who never was fully hand tame. And was terrified of a hand in the cage. Rather than a playpen, a large storage box can be good initially with a robo, with a bit of substrate (very thin layer or they just bury themselves and hide!) and a couple of toys. For a bit of hand taming and to get them used to coming out.
Seriously I had to virtually dismantle the cage to get ours out as he would flatten himself against the bars behind the wheel to avoid being picked up.
You could try a tube with a treat in but they are so fast and it may come to scooping her in a mug. Although it doesn't sound nice, once they're out they seem fine. Latterly I found something that worked for me for getting our robo out and that was a fuzzbutts snooze cube. Our robo absolutely loved that snooze cube and if I put it in the cage he would walk into it. And I could lift him out that way. But he was a bit older then and more used to me - still hated a hand in the cage though.
How you set the cage up can affect how easy or hard it is to get them out too. I had a cage with a big front opening door (which really really helped!) after giving up on a tank. And the house on the right with the entrance not far from the door so I could put the snooze cube near the house entrance and wait for him to come out and go in it.
As for cleaning the playpen between hamsters - I remember this topic coming up before and there were no clear answers. I would say, bearing in mind a taming box might be better to start with - no don't use the same items in the playpen. The playpen itself should be fine but I'd have separate toys for it for each of them if possible - and for the robo try a storage box first rather than a playpen. If the playpen has bars then yes a robo will escape!
As for weighing. Not easy. Those flat digital scales can make it easier. Put it in the base of the playpen box with a bit of cheese on top and zero it and see if the hamster investigates the cheese! Then read the scales.