Hello cjtursi1. Welcome to the Community!
Old houses can be fun, but maybe not so much when the plumbing rusts out...
A threaded "X" fitting for drains should actually be a galvanized steel cross that looks like this:
Cast Iron drains are not threaded. They use oakum packing and melted lead to seal connections. These are primarily used for the large, (4" and up), main stack and toilet drains in older homes.
In any event, if you have threaded fittings at the cross that are rusted and leaking, you will have to disassemble the cross and replace it. Along with the cross you will have to replace the pipes leading into it, as the pipe's threads are also damaged beyond repair.
The best way to do this would be to cut each of the 4 pipes out, and them unscrew them from their opposite end. In order to replace them you would need a pair of pipes for each one removed and a union like this to join them back together.
This is the best way to repair your drain.
Are there other options? Well that depends on what your local building codes allow.
There are other types of repair connectors that you may be able to use, either replacing the unions while using galvanized pipe, or by splicing in other piping material like PVC. The issue is a matter of building codes. Please call your local building inspector to see what is allowed in your area.
An example of an easier way would be flexible connectors like this one:
I hope this helps,
Newf.
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