I prefer wing-mans, even if they screw the things up they entertain the cockblockers, they don't need to engage them, they just need to talk to them.
So in this case i recommend you a wingman, that's why i get mine all the time. He's shitty but entertain well
About your main problem, that's because you engage them all and after you forget about them. They are not cockblocking you they are trying to get their attention back.
You have to gradually put them apart in this order:
- Approach and engage your obstacles neg your target
- Continue engaging your obstacles but stop negging your target and put her into your social bobble
- Engage anyone in the group (including your target)
- Start to engage only your target but don't ignore your obstacles.
- Grab your target's hand ask permission (to others) to take her just for a few minutes
- Isolate her from your obstacles and thats it