You're not upgrading that much if you're going from a 30-gallon to a 50-gallon Rubbermaid storage container (and these containers aren't meant to hold water). If you're going to try to have them together and you don't plan on getting a large tank, consider getting a stock tank to house them in.
Yeah. This is just a temporary housing being that it is cheap and effective. I will probably be getting a stock tank in the future, but might as well upgrade from a 30 gallon to a 50 and get myself a good filter in the process of it all. It's not like I'm making a big investment being that these storage containers are very cheap (under 20 dollars) so I might as well house them in the next best thing and then progress to whatever is next; plus, I do need the new filter. Both turt.s are about 2 inches in shell length, so unless I got something wrong it's 10 gallons for every inch (of course, more added for each turtle), so 50 gallons seems like a reasonable step forward until I am ready to get them something more permanent

BTW, I need some ideas on a basking area. I was thinking about the standard turtle dock that sticks to the wall of the tank by suction cups, but being this is a plastic tank, I'm not sure if it will work. If I don't find something that I think will work good, I will probably make one.