make sure all your cells are at the same voltage before you connect them in parallel. parallel up all the balance leads and then connect them to one 6S lead parallel up you to main discharge leads and then series the 2 packs together viola; one 6S 10,000mAh pack
(unfortunately I took this photo before I had connected the main discharge leads) https://esk8content.nyc3.digitaloceanspaces.com/uploads/db2454/original/3X/7/0/70ae0b5b721c822c4577fbf24a6779a0eae449ac.jpg