I agree with Dinahmo, that the media’s constant harping on about not being able to see your family makes us feel left out if our family members have made arrangements which don’t include us. Once again I say that so many people are not doing exactly what they want because they have to keep other people happy. Unless I’ve misunderstood, Grannylancs contacted her son’s in-laws to ask if they were invited, and, if that’s the case, I can understand if he was annoyed, especially as his dad called him to ‘ have a word’.
So, rather than be invited ‘ on sufferance’, I’d suggest inviting your son and his wife another day, and spending the day with your mother ( who , again if I’ve understood, will be alone). I’m sure you’ll be able to enjoy it.