You can keep reptiles in smaller enclosures if you let them out each day for a run around. I had a friend that kept his snakes and lizards in cages when he was at work and opened the cages when he got home. He did the snakes and lizards separately so they didn't eat each other but they got an hour or more of running around the house each day. Quite often his lizards and snakes would be all over the house for most of the time and he would be sitting on the couch with a couple of lizards on the top of the couch watching tele with him.
As long as the enclosure is big enough for the animal to move about and not knock its water container over, the smaller enclosure should be sufficient if you let the animal out each day for a run around. Try to confine them to one room and keep the door shut when you let them out. Otherwise they can get injured if they find something bad to eat (poisoned bug), soap, cleaning products, etc, or chew on power cables.
You can have climbing branches in the enclosure and your room. These can be branches from any non toxic plant, or you can make something out of wood from the hardware. Have lots of branches in the aquarium and it gives them more areas to hang out.
You can also make platforms or different levels in the enclosure. Use wood or Perspex legs and put a shelf on it so if gives them another level to hang out on.
Feed them a variety of foods including earthworms (make a worm farm and grow your own), crickets, cockroaches, mealworms (make a farm for them too), etc. Wingless fruit flies get eaten and can be cultured in plastic containers. Aphids can be collected from roses during spring and autumn. Weevil larvae and moths can be cultured in buckets or flour or rice. Basically, if it moves and is not poisonous, they eat it.
If the weather is warm you can feed them each day, but if it's cool, you only feed them once or twice a week. They need warmth to digest their food so if you keep them warm, you can feed them more often.
We use to chuck a handful of crickets into the cages and they ate as many as they could and the remaining crickets hid in the tank until they got eaten. However, their enclosures were kept warm, so don't feed them as much in cool weather. One or two crickets per week might be sufficient in cool weather but you might feed 20 crickets per week in hot weather. Some lizards will eat more than others too so offer a few at a time and wait until they have been eaten before offering more. If in doubt, err on the side of less is best. They don't need feeding everyday unless you are trying to grow them, bring them into breeding condition, or they are recovering from an illness and you are trying to build them back up.
You can sprinkle a reptile vitamin supplement on the food before offering it to them.
You can use the same tank for both lizards. The smaller one (Rankins) likes water so have a bigger water container for it.
If you are limited to space, get a double or triple tier stand and get aquariums that are 3ft long x 18inches wide x 18inches high. Make sure there is at least 8-10inches of space above the tank so you can work in it. Have a few branches and a shelf in there and that will give them heaps of room.