The months don't need to be consecutive  ...  read the rules in pub 501.

https://www.irs.gov/pub/irs-pdf/p501.pdf

IRS interview to help determine who can be claimed:

https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent

https://ttlc.intuit.com/questions/3113432-who-can-i-claim-as-my-dependent 

There are two rules to claim someone as a dependent on a tax return, either the Qualifying Child rules or the Qualifying Relative rules. 

Who can I claim as my dependent?

You can claim a child, relative, friend, or fiancé (etc.) as a dependent on your 2018 taxes as long as they meet the following requirements:

Qualifying child

• They are related to you.
• They aren't claimed as a dependent by someone else.
• They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They are under the age of 19 (or 24 for full-time students).
  • No age limit for permanently and totally disabled children.
• They live with you for more than half the year (exceptions apply*).
• They didn't provide more than half of their own support for the year.

Qualifying relative

• They don't have to be related to you (despite the name).
• They aren't claimed as a dependent by someone else.
• They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
• They aren’t filing a joint return with their spouse.
• They lived with you the entire year.
• They made less than $4,150 in 2018 ($4,250 in 2019).
• You provided more than half of their financial support.

When you add someone as a dependent, we'll ask a series of questions to make sure you can claim them.

*** Residency Test
To meet this test, your child must have lived
with you for more than half the year. There are
exceptions for temporary absences, children
who were born or died during the year, kidnapped children, and children of divorced or separated parents.
Temporary absences. Your child is considered to have lived with you during periods of
time when one of you, or both, are temporarily
absent due to special circumstances such as:
• Illness,
• Education,
• Business,
• Vacation,
• Military service, or
• Detention in a juvenile facility