Answer: The park cannot guarantee that health safety measures will be followed by everyone and it is not your job to police the stay-at-home order. There is little in the way of legal enforcement mechanisms that the park can use to enforce COVID-19 safety measures, particularly on the tenant’s own space.
The best that you can do is to remind residents that for the overall safety of everyone in the park, they should avoid congregating on anyone’s rental space. Your reminder could include the admonition that residents are obligated under Oregon law to notdisturb the peaceful enjoyment of the premises, and that gatherings right now pose a threat to that peaceful enjoyment. (With regard to visiting family members or guests, there is little you can do to prohibit that issue as long as they are not otherwise violating park rules.)
You do have more control over common areas such as playgrounds, recreational halls, swimming pools, etc. To the extent possible, you should close those areas to help reduce your risk of liability for any claims of negligence should someone become sick after using your park facilities. For common areas that are necessities, such as laundry rooms or restrooms, post and enforce reasonable social distancing requirements according to government recommended practices, and more regularly clean and sanitize those facilities.
If certain tenants or groups of tenants persist in gathering in an unsafe manner on their rental spaces, you might have good reason to issue a 30/14-day, for-cause eviction notice for disturbing the peaceful enjoyment of the premises. Or, if a tenant did something intentional like trying to cough on someone, for example, then you could probably issue a 24-hour eviction notice for “outrageous behavior.” However, as always, check with an attorney before issuing any eviction notices along these lines.