Fullback Volland and attacking midfielder Firmino have attracted enquiries from Liverpool this summer, where managing director Ian Ayre is understood to have registered their interest during a recent trip to Germany.
Everton boss Roberto Martinez is also a big admirer of Firmino.
However, Hoffenheim chief Alexander Rosen insisted: "We are not in a weak position.
"Both want to stay and will play next season with us."
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