I've been wondering myself if Astro will be the
only returning character, and that everyone else will be brand new. After all,
this is a different city that the series will take place in. If they wanted to, they could change the doctor who creates him into someone entirely new.
But then again, I have doubted myself thinking about that. I would think that there would be a desire by fans for other certain characters to return, so they probably wouldn't go the route of making an almost entirely new cast of characters. All I can say is that it'll be interesting to see who of the main characters will return and who won't. For all we know, they could pull a fast one on us and actually include an unexpected veteran character; I'm sure none of us would've guessed Ham Egg would've returned in LAB had they not included the promotional image for that right off the bat.
Based on the summary, it at least sounds like Astro's friends from previous series like Shibugaki and Tamao will not return if his two human best friends are entirely new.
As for Tobio, I'm predicting that he probably won't return. I'm wondering if they're going to change Astro's origin story a little bit in this iteration. I'm wondering if what Tetsuwan Penguin said in his post may be right, but we'll have to wait and see.