self sufficiency comes later when you have survived the initial event, a hunkering down period will be necessary first to make this happen for which a store of food and water will be required.
the only venomous snake we have in the UK is the Adder and cases of actually being bit are usually very rare, most times it will see you before you see it and be long gone before you get anywhere near.
20 people living in a house would be impossible, we'd need a huge house to start with, then there would be arguments, petty squabbles, to say nothing of disease which would rage through a household of such proximity.
