How do I identify and prioritise several contributory problems

It appears that My outside drain is blocked, there are issues with the the kitchen and bathroom sinks, (odour etc). The inside wall is very damp right next to the drain, however there is water pouring into my cellar with rainfall, coming from around the same area. (The council have visited and assured me that this is not their responsibility). My bath has been leaking for quite a while, causing water damage to the ceiling below. When the ceiling collapsed I had the leak fixed at the same time as getting it re - plastered. This lasted 2months before the leak re-surfaced as a slight drip. This has continued to the extent that there is a hole (approx 2") going through 2 floors and a staircase, to the concrete steps of the wet leaking cellar below! Today my toilet appears to be blocked beyond any conventional repair! Drainage expert, plumbing, or damp proofing specialist??,