First of all facts are incomplete. The nature of what you call is 'properties' is important, whether agricultural or non-agricultural. Also how he acquired the said properties is also important. The state in which each of the properties is situated is also a relevant issue.
Generally speaking, there are some restrictions in every state but different in details on transfer of agricultural properties,.
Assuming that the 'properties' are non-agricultural and not situated in Chennai, (going from the name of the querist), and further assuming that the grandfather had acquired these properties out of his own independent earnings, the answer is given as:
1. Except Chennai, in other towns/villages in South India, will executed already by the grandfather is not required to be compulsorily probated through court.
2.As a first step, applications are to be lodged with the Municipal Corporation/Municipality/ village Panchayat and the Tahsildar of the Taluk, where each property is situated, to get the revenue documents and record transferred in grandmother's name. Tahsildar comes into picture because of patta transfer, in vogue in tamilnadu and some other states.
3. The grandmother can meanwhile pending the formalities described, execute a will in favour of person of her choice. It should be written neatly or typed. There should be two witnesses, who are present together, at the time of signing the will. The witness should not be a beneficiary under the will or his direct descendant.The witness should also be a person who personally knows the 'testator', in this case, the grandmother.
4. Sometimes, will is challenged by other likely ligal heirs, who do not get benefit of the will, on grounds of force or undue influence or the 'unsoundness' of physical and mental faculty of the testator at the time of execution of the will. This may entail protracted litigation. To guard against this, I would suggest one or two deliberate mistakes in spellings of words in each page of the will, rectification of mistake by hand by striking the wrong word and re-writing above, the correctly spelt word. Each such correction should be authenticated by full signature on the margins. Additional precaution is to count the number of corrections on each page, write "no. of corrections -xxx' at the bottom of the page in testor's own handwriting with the signature of the testator.
Caution: Answer may be different if even one fact assumed differs.