I Think Your All Forgetting That They Can Only Be Fused For 30 Mins, I Donno If That Will Effect The Suggestion But Just A Reminder...Also What Your Suggesting Is A Little Much...Trunks + Goten...Think Of All The Added Animations .. Modelling...Everything..Plus The Strength Of Gotenks Would Have To Be Pretty High.. I'd Say Just Fusing To Gotenks Would Be Good Enough Transformation As It Is..But Goten + Trunks, Then Gotenks, Then SSJ Gotenks , Then SSJ3 Gotenks Would Be Much... Imagin When You Die As SSJ3 Gotenks..You'll Have To Transform All The Way Back Up, Talk About Transkill..Ppl Will Gladly Keep You From Reaching Gotenks...And Trunks And Goten Are Weak...Especially If Your Compairing To No.18 lol, If Goku Didnt Get That Damn Virus, He Would Have Easilly Defeated 16,17,18,19,And 20-Gero... Dont Forget Cell...Becuase He'd Still Be First Form.. 18 Could Never Touch Anyone..lol,
Trunks And Goten Are Goku And Vegeta's Desendants, Plus They Had Already Got To SSJ At A Very Early Age, Imagin How Far Behind 18's PL Is..For That Matter I Also Think Goten Would'nt Even Be Born.