What to do next?

you can do defoliation as they just start 2nd week of 12-12.. cut big leaves which cover the branches.. i would consider of removing leaves and branches which are weak and getting not enough sunlight .. all the top have to be level for more bigger top buds .. i would prefer LST but it seem your tent is so full and u don't have enough space to train them LST in tent .. just grab and take one pot by one outside and training is better .. after all, they look really good and healthy.. wish you have a good yield, grower love 🍀

If you are before day 21 of flower then yes defoliate. Remove big light blocking fan leaves. Don't worry you have plenty of solar panels on your plant. Removing some fan leaves is fine. If you are past week 3 of flower then stripping the plant of some of it's leaves can cause stress that will hinder your yield. If thats the case then leaf tucking is a better option. Just tuck the big light blocking leaves back as best you can. Just get them out of the way so light can get down into the canopy. Yes, you plants will stretch when inducing flower. How much depends on a lot of factors, but mainly genetics. Apparently introducing week 1 of flower nutrients while still in veg the final week before the flip can greatly reduce the plant stretch due to the increase in Phosphorous. To give you an example, I flip to 12/12 when my plants reach 12 inches in height. When they are maxed out and finished their stretch (week 4) they are 30 inches tall. Week 2 they will stretch like crazy. Week 3 they stretch still but much less, and by week 4 you may see another inch or 3 but it will stop and then you just ride the wave home. Other Stronger leaning sativa varieties can stretch a great deal, sometimes 3x. Indica's generally are a squat plant with broad leaves and are branchy and bushy.