Is there an advantage in being both a 501c3 and a 501c19
There is no tax advantages of being both 501c3 and 501c19 organization.
As long as the organization qualifies for either status - it will get exemption from federal income tax.
For donations to be deductible as charitable contributions on the donor's federal income tax return - 501c19 has additional requirements mentioned above.
If you are looking for any specific advantages or disadvantages - please clarify.
My organization is already a c19, but is thinking about becoming a c3. Both types offer specific advantages individually. However, we are not certain if it is advantageous to become both or convert to just c3 to be able to accept charitable contributions.
As long as the organization has either status - it is eligible to solicit and accept charitable contributions - so far having both statuses will not provide any additional advantage.
If you plan to drop 501c19 in future - and want the organization to be treated under 501c3 status - you might obtain both the second status - but tax wise - there is no any additional benefits
As I mentioned - the 501c19 organization has additional requirements for donations to be deductible as charitable contributions on the donor's federal income tax return - at least 90% of the organization's membership must consist of war veterans.
In case your organization doesn't met this test or will not met in future - having 501c3 status will protect your donors.
However - as long as the organization has either status and donations are deductible for donors - having both statuses instead on either one - will not give any additional benefits.