large hands (s) manus ingentes
grammatically correct, but ingens is a little more than "large".
by our senates nostris senatibus
to/for those hands of yours istiis manibus
istis, not istiis. the stem is ist- (not isti-) and the ending is -is.
to/for the other knee aliis genibus
"the other" should be translated by alter, since it implies there are two things in comparison. your English is also singular but your Latin is plural.
by the sweet fruits dulciis fructibus
dulcis, -e is third declension, so dulcibus.
flebile nescio quid queritur lyra, flebile lingua murmurat exanimis, respondent flebile ripae