Hi @poppyw
Welcome to the forum although I’m sorry you have had a cause to join 
There will be stroke support groups in the Brighton area that you can find from the Stroke associations map but beware it’s only stroke association groups and a lot of groups have reason not to be affiliated so unlisted but do exist.
Some groups will provide carer respite breaks.
Age UK and adult social services at the local council will both be able to advise with on the ground local information.
There is a post on benefits on the forum
and if you’re parents aren’t receiving pip and carers allowance (and are below retirement age) they should apply. The post mentions other benefits too That may help with mobility and enlisting carers.
Some of us on here run a Thursday afternoon online cafe and there is a fortnightly Friday online carers cafe and you and they are welcome at both/either
Others will be alone soon I’m sure and they will have other perspectives and advice 
Caio
Simon