Can a 55 and older association discriminate if grandparents living in the association?

A 55 and over community can permit children and residents under 55, but they are not required by law to do so.
By law, a 55/over community only requires 80% of residents to be over 55 to qualify for the tax breaks these properties get. But some are 100% 55/over by choice, in locations where it is not difficult to fill all residences with 55/over. If they do not permit under 55, it must be stated clearly in the CCRs.
However, if it goes to court, a lawyer getting a judge to grant a stay or injunction to prepare the case can delay it long enough to cover the deployment, but if the case is lost, the grandparents could get evicted after the deployment anyway.

Not sure if this would be covered under USERTA but its worth asking. I believe each State has an Employee Support of the Guard and Reserve Organization. I'm sure if you GOOGLE this you should be able to find the POC in your State, good luck!!

Look, HOA's are a bitch, often have their own rules, which are required to be signed off on before you move in. They make the news all the time over, not allowing the national colors on houses/apts, etc. It is not discrimination if they signed off on the rules. Older communities are set up for older folks, peace, quiet, etc. The grandparents need to talk 1 on 1 with the HOA, explain the problem and the duration and try to work a deal.