What instruments do the members of Houkago Tea Time use?
From Wikipedia, which cites specific episodes as references:

Yui: Heritage Cherry Sunburst Gibson Les Paul Standard electric guitar

Mio: Left-handed, 3-Color Sunburst Fender Jazz Bass with a tortoiseshell pickguard with  D'Addario EXL160M medium bass strings; in the first volume of the manga, Fender Precision Bass

Mugi: Korg Triton Extreme 76-key keyboard; in the first season's ending animation, Korg RK-100 keytar; in the second season's ending animation, Hammond organ

Ritsu: Yellow Rick Marotta Signature Yamaha Hipgig drum kit with a cymbal set from Avedis Zildjian; in the ending animation, white Yamaha Absolute Series drumkit

Azusa: Fender Mustang electric guitar