You’re in a tough place with your neighbor dropping by…and a hugger. One thing that may help is having a packet of masks hanging near your door. We do this at our house. I have a hook with a baggie of new masks. When someone comes unexpectedly and will be entering the house, we ask them to mask up.
Considering you’re in a senior housing setting can you put a little note on your apartment door that says Masks Required? I have friends who have done that where they live. Now when people drop by they know to wear a mask. Sometimes just being forewarned helps.

For a covid test, if you live in the US you’re able to get freebies from the government delivered with the postal service.
Here’s the link https://www.covid.gov/tests/
They arrive fairly quickly and then you’re prepared in case you feel the need to test.

I’m sorry you’re missing the grand 16th b-day of the twins but this can be an important learning lesson of thinking beyond themselves by having compassion and understanding for others.
You can let them know how much you love them, that you’re sad to be missing the celebration but that you have health concerns. Maybe they can visit (masked) with you in a quiet and not busy common area so that you can have your own little celebration with them. We had our daughter and son-in-law over the holidays for several days. All 4 of us were masked anytime we were indoors. We even ate at our small table together with masks on! 😂 We moved the mask down with bites and then right back up. That way we can laugh and talk fully at the table without spreading any aerosol across the table. It is a way of life and my family is very accepting. When my husband and I are alone, then we don’t need to mask. But with visitors…it’s just what needs to be done. I didn’t go through everything I endured the past few years to potentially succumb to a virus that is avoidable.

Stay strong for yourself. ☺️