I noticed my kitchen sink stopped up. Checked both downstairs toilets, one drained fine other didn't. Grabbed the plunger. Plunged the toilet @ North end of house & no results, went to toilet on South end of house no result. Went back to sink, filled up with water & then plunged it. Water went down. Back to the toilets. Both still would not drain after repeated attempts. For some reason looked in the crawl @ the South end of the house & sure enough there is water coming from the cast iron toilet drain. My question is would this leak cause the other toilet not to flush due to improper venting now or could I possibly have a bigger clog somewhere in the line or worse yet, possibly both are issues. Thanks, Jim

That leak is a bad wax ring under that toilet. It did not cause your issue but will let sewer water out when you plug or flush the other toilet. Replace the wax ring but you also have a clogged drain pipe which needs rodding, stop with the plunger, its of no use. The clog is downstream of the sink and both toilets, do you have a clean out anywhere? If no clean out pull the toilet farhest downstream, hope that's the one that needs the ring cause that one needs to be pulled to replace the ring anyway