Here is my $0.02 if your arrival date can be flexible by a day, since it is impossible to fly out on Independence Day.

On 7/3, AA has RIC -> MIA -> AUA for 11k + $5.60. Depart at 7am, arrive by 2pm. Same flight on 7/5 is 10k. Transfer 60k Marriott to AA for 25k miles, enough for two one way ticket to Aruba.

Coming back is a lot easier, from 7/10 - 7/12, United has AUA -> EWR -> RIC for 17.5k + $75 each. 4 pm departure, arrive at 10 pm. Transfer 35k UR to UA should cover it.

There's also a Hyatt place near Aruba airport for 8k/night, available from 7/3 - 7/10 if MIL's couch gets old.

Best of luck!