Yes, the Budgies and quaker get along. Not "I'm going to groom you" get along, but "we can sit here on the same perch within inches of each other and be content" get along. It absolutely floored me when I saw it.
Yoshi is so cage aggressive but one day while I let the budgies out to clean their cage and Yoshi was still in the room (she was being very, um...opinionated...that she did not want to leave her cage that day and go to the play stand in the other room) it got really quiet (budgies being completely quiet means trouble). I turned around and about had a heart attack because both little ones were in Yoshi's cage.
But then I realized my cranky little girl was acting
happy and even let me get her out of her cage by my hand when usually I need a wood dowel.
So they get limited time out together as a group. The Ring Necks are virtually cage free but have "their" stands. Yoshi has a cage, but its now kept open all of the time (a cage makes her feel more secure it seems). The budgies used to get let out after I moved the bigger guys to the play stand in my bedroom and then let them have a couple hours fly time every evening, but now they do get some time out with the big guys as well when I'm home.
Yes, its a risk and no I would not advise it for everyone, but for now this works for us. Right now I'm more worried about the two ring necks hurting each other more than I am about the budgies and quaker.