The carrier shouldnt be so underleveled, but the assisters should. (In this case, they should be underleveled, cause it just doesnt matter that much)
Assisters should usually go out to stack creep spots and to gank mid if possible, giving the carrier enough time to get some solo experience or dual lane experience in case only one assister is doing all that.
As to the cash, assisters should get it from pulling and last hitting those creeps (if its warded, counter that ward), getting kills assists and such.
If your trilane is against a dual lane, be agressive, and if you're failing at it, just disassemble your trilane, cause its going to be a snowball.
Tips to make it work: Make sure ur solos are confident about it and they can do a good job, use ur mic to coordinate your actions on the trilane. Make sure ur assisters carry tps at all times to help other lanes in ganks situations. Make sure the carrier is getting the most of it, kills, stacked creeps, and all the farm he can possibly do.
And the ultimate tip, make sure your carrier isnt retarded and will carry you guys if he gets all the farm he wants.
Basically the point of a trilane is usually to get the hero in it complete free farm. This includes giving them as much gold and XP as possible. Once you've started that advantage rolling, a good player can usually take care of himself, so the supports can leave the trilane and go ganking.
Usually a trilane against a weaker lane will play aggressively, getting kills and making sure the farming hero has a big advantage, then the support heroes will leave the lane to gank. If the farming hero is in trouble the supports or solos TP back in to countergank.
Competitive trilanes usually consist of a hero that can also solo effectively () and two supports that can leave the lane and gank with very few levels and little gold () for these reasons.
Originally Posted by Tripwyr
There is no way to force your team to become better. Your only option is to improve your own play; once you've improved your own play, your MMR will increase allowing you to play with other better players.