1.12.2 Forge Not Working After Brother Got 1.15 Forge

[Snokkus Maximus]

So A Few Weeks Age I Installed RLCraft Mod Pack For 1.12.2, And Got A Server With It. The Next Day, My Brother Had Tried To Install 1.15 Forge, And 1.12.2 Kept Crashing When I Opened It, So I Had To Delete Those Mod Files, And 1.12.2 Worked Again. Then My Brother looked Up How To Get 2 Versions Of Forge, But When That Happened, 1.12.2 Didn't Work Again. He Fixed 1.12.2 So That The Title Screen Was Glitched But Minecraft Worked, Though I Found Out That in 1.12.2 My Fps Is High, Like 86 fps, But Some OF My Settings Are Gone, You Can't Hit Mobs, The Inventory Is Glitched, And Dropped Items Are Very Laggy. Im meeting up with my friedns in an hour, and i really want to be able to play with my friends. Pls Help....

Edited April 18, 2020 by Snokkus Maximus