Young dogs suddenly attacking old dog

Does anyone have any experience with this? Out of the blue today my two young dogs have started attacking my old dog (14). The female starts then the other joins in and we have to separate them (my husband got bit in the process). There was a bit of blood drawn the second time (honestly not sure from which dog, they're all pretty fluffy), a lot of yelping from the old dog, and the 85lb 1yo was latched to the help'em up harness from our old dog and wouldn't let go (he broke a clip)... my husband eventually got him off (I can pick up the female no problem) but we have to close the gate or they go right back to it... They did ok for a bit after a time out, then went back at it again... again the female started it... They're separated right now but I really don't know how to deal with this long term (we have a gate to the family room where we spend most of the time, but the rest of the floor is very open space, and the door to the backyard is in the dining room - and they all sleep upstairs with us).

Our old dog is going to the vet later anyway (for a blood draw but I want to see if they can check him out while they are at it), and he's not been doing well, and I know that sometimes dogs smell when a dog is sick and attack them... but I'm seriously worried.

Thoughts?