Matt Pinfield's girlfriend and brother say the former MTV host is more communicative than his daughter is letting on ... because he was singing along to music during a recent hospital visit.

Matt's daughter Jessica claims he's incompetent and needs a conservatorship after suffering a stroke ... but his girlfriend, Kara Brown, and his brother, Glenn, say they're being iced out and cut off by Jessica.

Kara and Glenn's attorney, Todd Wolfe, tells TMZ ... Kara had an in-person visit with Matt at Kaiser Permanente L.A. Medical Center on Friday afternoon, with Glenn beaming in on video.

Todd says he was there too and tells us Matt was significantly more communicative than they had been led to believe.

We're told Todd brought a portable turntable and Kara brought a bunch of records ... and Matt lit up with delight when they started playing him music.

Todd says Matt even sang along with Kara to some Elvis Costello ... telling us the whole interaction was "beautiful."

TMZ broke the story ... Jessica claims Matt is unable to make decisions about his health and finances, and she filed for a temporary conservatorship to oversee his bank accounts for fear his girlfriend will siphon the funds.

Kara and Glenn beg to differ ... Kara says she doesn't have access to his money and claims Jessica got her thrown out of the hospital. Glenn says Jessica has been isolating Matt from the rest of his family.

A judge ruled Thursday Kara, Glenn and their attorney are now allowed to visit Matt in the hospital ... and it sounds like the first visit went better than expected.

The family battle is in full swing ... and now Kara and Glenn say they have some more ammo in their war against Matt's daughter.