@Bikram Gurung, I haven't applied for my parents yet. They are in 80s, and still pondering if I should have them apply for visitor visa or not.
WIth resepect to yours, it would be safe to take some documents such as property information, latest bank balance statement etc. in case if they ask.
I would also send a letter from you explaining the intention of visit, and financial support documents (Affidavit of Support), and your bank statements.
If they already got 10 years visa and were here before and they went back, my expectation is that consular would not be asking for much info.