Anticipatory anxiety in 3 year old

[fulltimedaddy]

Not really sure where to start with this, but I’m wondering if anyone has any experience of anticipatory anxiety in toddlers,
From being around four months old our son would cry whenever anyone walked into the house, he’d cry if we took him to see family, but he’s always been really happy with me and my wife, as he grew older, family stopped calling round as much, but he developed a good relationship with my MIL, she’s looked after him since he was around one year old, and he loves seeing her or going to her house, he’s now three years old and petrified of going anywhere else or seeing anyone other than MIL,
My mum has looked after him a few times for us and she says he always settles nicely after a while, but I don’t know how to help his anxiety of him trying new things or going to see people, I recently told him we were going to visit Nannan, and he must have asked me about it around 50 times, it’s always the same “I don’t want to go to nannans” “can we not go to nannans?” “Daddy.. will nannan not be there?” “Daddy.. can we stay at home?” “I want to stay here with you daddy”
When we get there within a few minutes he’s happily playing, but then seems to forget it all by the next time we have to visit.
He’s terrified of going to nursery in September, to the point that we don’t talk about it much anymore, no matter how we try to reassure him, nothing really seems to work.
He’s also still very clingy, he very rarely plays on his own, craves attention from us, even in places like parks or soft play, he drags us round all of the equipment, if I suggest doing anything on his own, Like going on a little ride etc, he’d rather just not do it.
All of this is compounded by the fact that his two nieces are basically the perfect children, everyone loves them, and they will literally go to anyone, and have done so from being babies.. so I feel like everyone in the family just seem to favour them, during lockdown we only got one Skype call with my parents, but I found out they were skyping my sister to see the girls every week, and as soon as they were physically able to, they went round to see them.. my son was an afterthought a few weeks later.
He’s such a lovely little boy, and everyone who meets him loves him, yesterday he was asking everyone in a shop what their name was and asked what they’d been doing today, 😂
so I don’t think it’s a confidence issue, I’m just at my wits end with the anxiety and the clinginess