A piece of advice I got years ago was "if you're not embarrassed by the size of your first bid, then you're offering too much"
The house has been on the market since Feb and has had no offers. Therefore, by definition it is overpriced. No question about it. Put your lowest offer in. I'd go E10k lower than you are thinking, just for to plant that idea that they are looking for way OTT. All your first bid is really doing, is letting the buyer know that you're interested. This is a very high stakes game of poker.
Let them take the hump if they want. The fact that they haven't had any other offers should concentrate their mind a bit. Nothing to stop you coming back in a months time and up your offer a little bit. If they don't succeed in selling in the next few weeks, they haven't a chance of selling until next Spring and with all the international global uncertainty, it's very likely that they still won't be able to sell at anywhere that price then.
It's unfortunate that there are resident tenants. This takes a lot of pressure off the seller as it is producing an income. If, on the other hand the seller wanted to move and was in a chain, they would be more likely to come down to a more realistic price quickly.