Soak your citrus for a few minutes in warm water with a bit of vinegar added, then scrub well under running water. You will be cooking with the rinds, so you want to remove any chemicals or debris that might be on the rind.
Peel your Blood Oranges. It is easiest to cut a thin slice off the top and bottom of each orange and then gently cut through the rind creating 1/4" segments all the way around, then peeling it off in segments.
Lay the segments down one by one and using a sharp knife carefully cut off the pith. The blade should be level with the counter and you will use a slight sawing motion. Cutting off the pith reduces the bitterness of the finished marmalade (although there is still plenty of bite).
Stack several segments of rind on top of each other and slice into very thin matchsticks. Continue until you have 3 C of thinly sliced rind.
Take your Blood Orange pulp segments and gently pull off as much of the white pith as possible. Chop the pulp until you have 3 1/2 C.
Slice your Meyers Lemons into segments, deseeding as you go. Cut the segments (rind & pulp together) into very thin slices.
Place all of your pulp and rind into a large stock pot and add the water.
Bring to a simmer, cook 5 minutes and then set aside in a cool place for 12-18 hours.
Put the mixture back on the stove and bring to a boil. Cook for 30-45 minutes, until rind is tender. Now it's time to measure your pulp/rind/water mixture. Find a pot or bowl large enough to hold all of it. Careful transfer your hot mixture into that bowl. Using a measuring cup, measure the liquid/pulp back into the pot. Add 1 C of sugar for each cup of liquid/pulp. Stir well.
Cool overnight in a draft free area. Check your seals, label and store!