Vegging Length

Hello, i have two plants that are 50 days in and they are both about a foot tall give or take a few . About a week ago i added two sprouted seedlings, i was wondering can i veg my original two plants until my seedlings get to a foot tall then flower them all together, or is that to much vegging for my 50 day old plants, thanks alot

i would flower the older plants now as they will most likely double or triple in size when you flower

Alright thanks for the input!!