The only way a Double ADC bot lane would work is if you have a utility ADC as your support. The ultility ADC that is playing support would basically do nothing but harass the enemy as much as possible and offer the utility for peel late game. As far as sharing CS between the 2 carries...that is really up to you, though it's probably better to have your main ADC farm during the lane phase, have your "support" adc grab coin to get some gold from the lane CS and just hope for kills. Maybe it's smarter for your main carry ADC get the farm, but when you get into the 2v2 fights, try to give the kills over to your utility "support" adc. Though I wouldn't finish Coin, I'd just get coin on the utility adc and then rush a Sightstone on the first back...then go full normal ADC build afterwards.
As for which ADCs would work best with eachother...Maybe have your main adc being a hyper carry while ofc your support adc a utility adc.
Utility ADC that might work "ok" as a support:
Possibly the best ADC that can be played as a support. In-fact her secondary role is Support since she offers the highest amount of slows and a strong stun for peel. Plus her vision with her hawkshot is very important.
This one could be argued of being a decent one. With her % health damage, and scouting abilities she can still be helpful in lane. As for team fights and forms of peel, she still has a slow and her Ult can be amazing for when the enemy team jumps on your main carry.
I don't know about her for a support adc, but she does offer a snare, slow and a lot of strong poke on top of a very powerful global ultimate. Her peel wouldn't be there for the main adc though.
Would offer the highest amount of safe poke on the list, and a more reliable slow than Jinx/Kalista. He wouldn't have much for pre-6 for peel but his ultimate is possibly the strongest form of peel for a carry when team fights come around, though hitting his ult would probably be the hardest.
Those are the ADC's that I consider "utility" adc that might be alright as a support. Though I wouldn't suggest doing double ADC bot lane. If you really want 2 adcs in the same game, then it's best to send one of them Mid or Top though and even then you would need a very strong peeling support to make those work tbh.