At the moment there are no rules for the beach apart from social distancing yourselves. There is a time limit for parking though of 4 hours - the green dotted lines where this applies are clearly shoen. There is a useful site here
https://playas.cempol.es/#!/Localidad/ to check the capacity of each beach (constantly updated)
99% of the bars and restaurants are open, with social distancing enforced obviously. Masks have to be worn in all supermarkets, public transport, public buildings and on entering bars and restaurants. Once sat at the table you can remove them, but if you get up from your chair you need to put them back on. You need to carry your mask at all times, but only need to wear it if you cannot maintain the 1.5m social distancing rules. All in all, it's fine, your relatives will have a great time!
