We have ancsetral property in name of our grandmother. Since she is expired and father and his siblings inherit the same. My father now wants to register his part in his name.but since his brothers do not want the registry for the time being, we find no other to do the same. Please suggest us the way if we alone can register our part only. Secondly can we sell our part without registry? Please guide us the process.

If this is in India or nearby country, I and others who are regularly on this site don't know the laws there, which are very different from Europe, US, Canada, and Australia.
I can't imagine how you can register a partial share of the land, much less sell it, without formally defining the actual boundaries of each share. That would mean hiring a surveyor, and it often means negotiating with each other to exchange areas that are not easy to partition into nice neat rectangles. It's a lot of work. Depending on how many siblings there are, you may find that the only feasible solution is to wait until all of you want to sell. And often the property is worth more as a whole anyway.
Another approach is for one sibling to get a short term bank loan to buy the others out, and put it up for sale immediately, assuming that you know that it will sell quickly.

ANY question on law needs to include your general locale as laws vary by area.

Part of this depends on the wording of the will if there is one. The will might not allow a partition. But the only way to deal with his portion is to sue for a partition of the property. And that might not be allowed according to local laws.