I am thinking to buy this phone due to my budget around $200 mark using this deal https://www.ozbargain.com.au/node/742436
I know this phone is 4+yrs old and will likely have not any software updates soon but do you see any concerns for using them in general for parents (battery, storage, camera are imp).
It was a great phone but now there are a lot of bargain phones new in the same price range that offer as good or better hardware specs these days.
The biggest concern would be battery unless it has been replaced as its very likely heading towards the end of usable life if its been daily driven and they are not the easiest / cheapest phones to service. The other is updates as you highlighted. You just need to make sure the user experience / clean android feeling is worth the risk of needing to pay for a new battery and doing without updates compared to buying a $200 new phone.