how to distribute the weight in the panniers to equalize our speeds.
If you are going to carry a tent and/or stove, those are obvious thing to give him. You are going to want to keep certain stuff with you in case you get accidentally separated. Keep some money, some food, your water, a map, your tire patching stuff, your cell phone, and some warmer clothes if there is any chance of it getting cold. He can carry the toiletries, non-essential drugs, camping stuff, spare clothes (including all off-bike clothes for both of you), and extra tools and parts. This might enable you to use only one pair of panniers. You might experiment with using only small front panniers, with perhaps a small bag strapped to the top of the rear rack. This will save you the weight of the extra pair of panniers, which can be significant all by itself.
You can only equal out the speeds somewhat, however, with weight. There's a good chance he'll still be faster. You should decide in advance what strategy you'll use. Will you ride together at all times? Will you stay in sight? Will you meet at the top of the hill? or the next town? or a preselected restaurant? If you do agree to sometimes ride out of sight, then I suggest that whenever one of you stops, you leave the bike in clear sight by the side of the road so that there's little chance of the other one passes by without noticing.
What’s the best way to break up our daily rides so we can keep going day after day?
Stop frequently, at least once an hour. Have something to eat before you start. Then start early. Stop for a second breakfast. Take a break for lunch. Stop at points of interest. Take a small side hike. Overnight, get lots of sleep--at least an hour more than you do at home.