I thought I would reply to this too because I am a 38 year old single mother with an eleven year old son who likes to bunk in my room, despite also having a great room with loads of cool stuff in it.
He runs around the house in his boxers...SO WHAT? Most mothers have been seeing their kids naked from day one its not as though its a big thrill, my son has occasionally seen glimpses of me in the nick but once again retreated immediately because he really isn't into looking at his mother naked.
What we are into is catching up and being close and as we both have very busy work/school lives and social lives plus lots of different interests, one good way to do this is have a late night zonk out chat in my big bed.
Lots of other cultures think nothing of mothers sleeping with their children I don't see what the issue is. If the children want to drop by for a chat and a sharing snooze, in order to restore closeness, safety and contact how is that an issue?
My son is a gregarious charger in his outward life, very popular, a keen surfer and extrovert. But the lovely thing about him is that he is able to say "I love you" both to me and his father in public and mean it and have no shame about doing so.
I think this is because we have always given him freedom to move as far away as he needs too emotionally or return as when he sees fit. We have let him ask for his requirements rather than dictating what they should be.
I think your cousin sounds like a great provider and a good mother why don't you ask her son why it is he likes to sleep in his Moms bed.
My son would tell you "Cos we talk about stuff and it feels cozy" I now because I have asked him why he still likes to drop by regularly.