Recently I am observing that many papers uploaded in RG were published long back in Nelumbo and in one case I found that both authors have passed away long back. From whose account they have been uploaded and who will attend the full-text requests?
There are several possibilities for this, e.g. that ResearchGate has an agreement with the publisher or the journal. Could you please provide a link to this specific paper with two deceased authors or send its title?
As none of the authors has a profile in RG, it cannot be that someone (knowing their password) added this "by hand". I guess ResearchGate has taken the bibliographic information from the journal's website. Perhaps they have a partnership with the Botanical Survey of India so that all papers are listed automatically in ResearchGate. See https://www.researchgate.net/press-newsroom for examples of such partnerships.