Soupy - the laws of a religion having been in existance for thousands of years do not change to accomodate 20th C inventions or dictates. The rabbis are well versed in dealing with questions which come up as a result of changes in life situations or technological advances. They do this without changing the religion at all.
To answer some of your points:
1 Having a light shining in a stairwell 24 hours a day would piss you off. REally? Presuming you were asleep in your bedroom , a light from the hall shining through what must be a tiny chink in your front door would make you feel that strongly. Even if it did , what this couple are proposing is not that a light is kept on 24 hours per day. Prior to the sensor being installed there was no light at all. The couple are proposing an override switch. That is all.
2 The other leaseholders paying legal costs. As a Property solicitor I cannot see how this is the case. Leases do not provide for leaseholders to pay anyone's legal costs and that includes the landlord's. Furthermore service charges are subject to stringent regulation and easy to challenge and landlords are aware of this. I very much suspect this point was made to stir up the other residents against this couple and intensify media interest.
3 Practice religion in your home not in public places - this couple did, yes. They were forced however to bring this into public debate since something done in their immediate environment is forcing them to either cease using their flat or violate the sabbath. They are simply asking for eiter the status quo to be returned ( remember they did not ask for or make the change - it was forced on them) or for a change to be implemented which would safeguard their religious practices but not have an impact on residents.
If your argument as to following religious practices at home only is followed to the extreme then presumably muslim girls should not be allowed niqab or hijab at School and Christain religious festivals should not be celebrated in public. I do not agree with this analogy and believe that part of being a tolerant and multicultural society is allwoing relious practices to take place in public.