Question on ILR qualifying period

Hi
I have a question about my Tier 2 general dependent family visa and THEIR eligibility to UK ILR , My family member visa is issued on 14 July 2014 , valid till 31 August 2019 and they entered UK on 11 October 2014 .
My own tier 2 general visa issued on same day but I come first to UK on August 4,2014 ..so there is no issue expected with my ILR process.
Question is for my family members : is the ILR 5 years counted from date visa issued or from date they entered UK ?

If it's from date of visa issue ..is this means my family is totally eligible to apply for ILR any date after July 14 this year 2019 even if they come 3 months after visa issue and they will not complete 5 years before visa expires on August 31 ?

If it's from date of entry ..how an extension can be done ?

Thanks

All pbs visas and pbs dependent visa count from visa issue date.