Parents traveling to US on visitor visa twice without 6 months gap in between

[Suresh83]

My parents have multiple entry 10 year visitor visa. They were here from 21-Jan'17 to 6-July'17 

They now want to come for 2 months from Oct - Dec 2017. 
Will the second travel in 2017 be impacted because there isn't a 6 months gap between the two trips? 
Are there any recommended docs that can be shown at port of entry to confirm that there is no immigration intent? 

[Neda]

They can visit, but their I94 will be issued for less period of time.

[Suresh83]

Thank You :)

[JoeF]

They may get denied entry or they may get less than 6 months on the I-94. This depends on the officer at the POE.

There is no fixed rule about the gap between visits, but it is recommended to be outside the US for twice as long as the last visit was before visiting again.

[pontevecchio]

It is extremely unlikely to be denied entry. If they meet up with a particular mindset, they may face a few uncomfortable moments and be given a shorter stay. Which Airport are they arriving at? This is of great importance in the ease of entry.