Posted: 28/07/2017 at 14:09
If they're only concerned about the weeds & moss I'd consider using one of the lawn maintenance companies.
I used one until 6 years ago when I moved from my previous garden. The lawn area there was quite a bit larger than your parents & they charged £30 a time to visit 4 times a year and apply appropriate lawn feed / weedkiller / mosskiller. I could have had them once a year / twice a year - whatever I chose - but the lawn was in a right state so I went for 4 times.
The charge was less than I would have paid if I'd bought the feed / herbicides myself from a GC and they came and actually did the job - where I would have sat and looked at the box of chemicals for weeks and maybe only done it once a year.
I also paid them a one off fee to scarify and aerate the grass the first autumn I used them.
The result was a proper, green, virtually weed-free lawn instead of the compacted weed-ridden grass which was there before. In some areas it was just compacted mud and weeds - no grass.
They really turned the lawn around & I shall be using them again now my new garden is nearly sorted.
Highly flexible / easily cancelled contract - no real catches with the company I used and they always gave me about 3 days notice when they were coming in case it wasn't convenient or I wanted to cancel.
The company I used was local to me (Suffolk) and was called Lawn Hopper or something like. Lots of other companies with names like Green Thumb, Green Man etc. Google is your friend