I'm widowed too. One of the most surprising things I've found is how many people have an opinion on how a widow should behave. It's hard. And dealing with their expectations as well as one's grief (and for you, a baby) is almost impossible. So although it isn't easy, it will be best for you and your child if you set some boundaries. I did a lot of 'smile and nod and discount the advice/lecture you're giving me while letting you think I'm considering it' because it's easier than confrontation of telling them to fuck off for telling you who you can or cannot have coffee with.
Just because your husband died doesn't mean his friends are in loco parentis. Trustee does not trump mother. You're in charge of your life and your baby's and that is really important after the lack of control you had with your DH's illness and death.
I find it hard to understand the money stuff - so one of his friends inherited a house from him and will leave that money in turn to his own children presumably? It has bypassed you and your son? Whatever the details of it all, it sounds like you and your DH had rather an unusual financial set up for this day and age, and this may feed into his friends thinking that you are not capable of living your life/raising your son without their involvement.
If I were you I would give yourself some space by getting someone else to say to them that you're struggling with being social at the moment and please not to turn up unannounced. You could also use your son's sleep routine as an excuse.
If you want to you could set up times for them to see your son - at a soft play centre or other neutral venue (not your home) every month or so.
When you feel ready you should see a decent grief counsellor.
Also, please, if you're in the U.K., join Way If you're in another country then see if there is something similar for young widow/ers.
Love, they died, we didn't. The pain is agonising and I can't promise it gets better because it hasn't for me (almost 2 years on). But it does compress, somehow, so there is more space for other emotions alongside the grief, and it is possible to be happy and sad all the the same time. I am now. Many days the happiness even eclipses the sadness.
Look after yourself and your child first. 