By spawning do you mean they have laid eggs and are guarding them? If not, I have a couple pairs of angels start to clear the tank and then not actually spawn, ever. Also, I had a pair of Marbles that were in a highly neglected tank with a bum filter and an algae problem. They spawned and one promptly died. But now I have two pairs of angels who spawn regularly for me. The links above do give a lot of info. So, I will only add what I have done.
My first pair spawned in a community 75g planted tank while I was on vacation. They didin't really kill any of the other fish, luckily. When I saw them the babies they were wrigglers on a sword leaf. So, I promptly set up a 30g i had lying around to put them in. For you I would just try to find an Opaque divider to put in the tank. the clear ones work, but they agitate the parents a little being able to see the other angels. I then let the parents defend the wrigglers, which they did well. I waited for the 30 to stabilize as best I could and for the babies to be free swimming. Then I transfered the babies AND the parents to the thirty. Parent raising Angelfish is one of the coolest things in fish keeping. I highly recommend it if your parents will do it. I have read some Angels don't know how. Then, I letthe babies grow up to a saleable size withthe paents. It was so cool, everytime I would walk by the tank one of the parents would try to come out of thetank to get at me. ONe time one of the parents actually lept out of the tank after me when I was feeding. Now, I have a divider in the 30g and have a pair on each side that spawn about every 6 weeks. They're slower than others because I leave the fry in tank for about 3 weeks because I love the parenting. Then into a divided 55 gallon until they get about half dollar size and I sell them to LFS for store credit. Its really fun and Angels will handle a wide variety of water conditions, but IME softer water makes for faster growth.
So, for you I would get the divider first. Unless you are going to get another tank. Then, read up on hatching baby brine shrimp. They will eat those right from the start, and they will grow amazingly fast. Also, don't wait on the water changes. I change 50% twice a week in my tanks.