Separation of an analog and digital power
You do not need to seperate analogue and digital supplies as such, but you do need to make sure all supplies are good enough. As digital supplies are generally noisy, and tolerant of noise, and analogue supplies tend to be quiet, and intolerant of noise, a reasonable approximation is to seperate the supplies on that basis, but it's neither necessary, nor is it often sufficient.

Filters used between the supplies can work well. Pi filters have Cs to ground at input and output, which can support large noise currents and so run you into other troubles, tee filters are generally more tame. The series elements can be inductors, resistors, or impeders, which are inductors made on a lossy ferrite that goes resistive above typically 1MHz, very handy for mopping up RF.

But the supplies are the easy bit. More difficult is the grounding, and the ground currents. The statement of what you need to do is simple, make sure that no ground currents flowing impose a voltage anywhere they shouldn't. To do that though, you need to know where they're flowing. Above a reasonable frequency (10's to 100s kHz), ground currents flow under the signal track, in response to the signal current. Don't break those current paths by gouging out slots from your ground plane.

A star ground is a commonly proposed method for dealing with multiple grounds, and will often work without understanding too much what's going on. With multiple devices however, it's not obvious how to apply it, and you need to go back to the fundamentals of ground current flow.