Be gentle with yourself, Sisabel. Remembering and feeling past hurts is sometimes necessary. There are no "needs to" and "must do" where emotions are concerned.
I would think that being cautious and guarded is not necessarily out of line after a decade of quasi estrangement(?). Knowing how you feel you can in turn be mindful of not letting it ooze out of you during these days where they are staying with you.
I think it's great that with a new baby the need for family has been reprioritized. What about the other grandmother, is she in the picture?