Yeh you'd normally try to find at least one homeschool group that you mesh with and that serves various purposes of parental support (parents gotta make friends too XD) and social/group development. There are some groups that might be social only but a lot will probably do some education support stuff. When mine were little we went to one that had craft activities and a different parent volunteer led activity for those that wanted to participate. In another one we went to more recently, there were classes set up for different age ranges that could be enrolled into and that had a more traditional "school" feel where they sat at desks and did worksheets, difference being there were short breaks between classes and you just enrolled in whatever you liked (you could also enrol social only in that group if you wanted).
Then youngest became a problem child and basically kept refusing to go because reasons so we're back to doing our own thing.
Excursions can be harder to organise for a group (been there done that, ergh I'm the worst person for this job) but there's a lot of benefits of being able to experience something fun with your friends and also group discounts and a lot of places have educational programs that can be accessed by homeschool groups with a minimum number. When I started organising group excursions there were a lot of places that couldn't cope with mixed age groups but other places were great and I did notice that things got slowly better over time.
There may be some people who may not have a lot of contact with the outside world because they're severely introverted, there's other issues or the parents are control freaks. I don't think I've met any of them but somehow that stereotype was the most common one for homeschooling for a while.
this is not counting kids who go through phases, all of my kids had a short period of time where they just didn't want to go out much and I had to practically force them on excursions because all of them loathed bookwork and absolutely refused to do it once they got to upper primary
There's a lot of online resources and a lot of groups will have a website (or at least a stupid Facebook presence). If your brother is on here as well throw him at Home Edders, there's a lot of young homeschooling parents on there with plenty of great ideas at the moment (and a couple of us with older kids with different ideas for older kids or in my case "this is an example of what your life could look like").