Visit Visa

Your question is not clear.   

What is the kind of visa you have?   for normal family visit visas, they are valid for use within 3 months and you get one month stay from date of entry.  Then you can renew relatively easily two more times.   

If your end date is fixed, then the two months should start from 18th of April.

But I am still confused about what you are actually asking.

thanks for quick reply, let me explain.

i am planing to bring my family on Visit Visa, if i book ticket 18/04/2018, i will get visa for one month i.e up to 17/05/2018 or 18/05/2018 (not confirm), then i have to renew for one more month as extension i.e 17/06/2018 or 18/05/2018 (not confirm).

my question is that i have fixed date to return my family i.e on 18/06/2018, so please suggest me if i book arrival flight date on 18/04/2018, will they can stay here up to 18/06/2018.

i don't want to extent for 3rd month.

please advice.

The stay given is 30 days from date of entry inclusive.   April is a month of 30 days so if they arrive on 18th, they get it till 17th (to be safe).  When you renew, May is a month of 31 days, so they will be able to stay till 15th.   That's my rough calculation.