After the demise of your grandfather, all his properties devolved into four equal shares, one each to his three sons and one daughter in law. However, since no partition was ever done between the four beneficiaries(as it appears), the property/ies continue to remain undivided. Despite this, it was free for your aunt(now deceased) to have passed her undivided 1/4 share in the properties left behind by your grandfather; a right which she has exercised and there appears to be nothing wrong in it.