So I have grown a Meyer lemon and regular lemon tree from seed. It has been 6 years and I have not had any fruit production. I will say the trees were despirately short on nutrition for a while until I realized it recently and started to use potted fertilizer stakes. Now they are a lovely deep green. I have several questions.

Do they need to be grafted to bear fruit? Or have I solved the biggest issue with improving the nutrition for the trees.

How and when should pruning take place? I live in Pennsylvania so the trees come inside when it starts to drop below 50 degrees. I've been reading and lots of things say it depends on the climate for when you should prune but they just say cold or warm climate. Not sure what my situation counts as. Any help would be greatly appreciated.