Your own family, must miss you and your son.
They do not have access to you or your son, like your in-laws do etc.
I would, refocus and spend time with your family.
You are the one, that decided to be around the in-laws.
They now seem to think you "owe" them, for all that they have done. And maybe they are tired of it. Who knows.
But they seem to have gotten less in patience. All around.
You did a lot as a Wife before your Husband died, and for your in-laws being with them, since then.
But maybe you just need to re-evaluate all of that.
Not that you cut them off, but you and your son also have to know your own, family too. And fortunately, your own Mom does not grumble about... how much are are with the in-laws and not them etc.
Your Husband passed.
But that does not mean, you have to live your life, in your in-laws realm forever. They seem to have done a lot for you/your son. And they see you as just going running/doing marathons all the time. And they are now, making comments about it.
This is like cold water in your face. But, it is also an indication that they are maybe getting tired of it. And sure, maybe they think they "own" you because they have done so much for you and your son. So you need to think about that.
Or maybe they need more appreciation.
I would not expect them to keep doing so much. I would start to change your routines with them. And be more independent from them.
But not in a rude manner. They have done a lot for you and your son, after all. But that does not mean you owe them for the rest of you life.
And they also have to realize that everyone has different ways of living.
You can live your life. BUT up until now, you have chosen... to be among your in-laws. And to have them do things for your son and babysitting and you chose....to be a heavy part of your Husband's family. And so, you ALSO... have set up this "routine" and dynamic with them.
But now you feel, shackled by it.
It is not only their fault.
And aside from that: they do not see your running or marathons as a priority. But you do. And they do babysit a lot, for you.
That is what they, see.