I agree with The Victorian, faffing about with tarps is ok over Christmas because you can't get a builder but 2 years is just not on.
What will your insurance company say when you have two ceilings down and claim for bedroom and lounge furniture? "Oh dear so you didn't maintain your property have you read your T&C? Sorry we are rejecting your claim".
Sorry to be a wet blanket but do think about some means of getting it done ASAP.
I would highly recommend you install new slates instead of doing patch work. Your roof is really old and even though you'll get it fixed, the problem will resume after a while.
I suggest you start looking for roofing specialists that can provide you with good deal of price for new roof.
There are a lot out there. You just have to have patience when looking for one. Ask your friends and relatives too if they can recommend someone. Perhaps you can also get discount from their referrals.
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