Hello; Thanks for submitting your garden and landscaping questions to the University of Maryland Ask Extension Service. 
II believe the bug in question is a harlequin bug. These insects are very common in late summer and fall. They can be a problem when they seek shelter during first frost and tend to congregate on sides of buildings and doors to get warmth from late afternoon sun. They may even find shelter inside of homes seeking warmth at night. More information to follow. 

Hello again; Looking again at your submitted images, I think a better identification of your insect is a box elder bug (Boisea trivittatus). Please see this University of Minnesota Extension web page on these critters: https://extension.umn.edu/nuisance-insects/boxelder-bugs. 

As I mentioned in my prior post they are not prevalent this early in spring unless they were able to overwinter in cracks and crevices within your Dad's house. The important advice is not to squash them as they can stain rugs and surfaces, but try to vacuum them from walls and doors. They do not bite but their presence in masse is concerning, and your Dad might see them again in fall when these bugs look for a warm hiding place again this winter. 

Good luck in your gardening efforts. Thanks; Christopher