HELP NEEDED..UK Visitor Visa for Special Needs adult

Hi.

I have to apply UK Visitor visa for my mother in law and her special needs adult daughter (who is dependent on my mother in law due to her attachment, epilepsy and she can't speak, she has siblings in Pakistan but they won't be able to manage her without mother,).

I need advice to make my case strong as how to apply together as i am in doubt as based on this reason they may reject Visit visas for both of them. Also if visa rejected i also have doubt she might not be able to apply alone later due to her history (as rejection due to dependency).

Also to mention as reason for them to come here is just to spend time with family here.

We are British national and working professional so not sure this make any difference in application.

thanks in advance.

The key is to show visitors have strong ties to home country and will return home after the visit.