It completely depends on the situation. Most people believe 'about a year' is the "right" number...but it's not really. There are some people who take much longer than that to get through the grieving process before they can even imagine dating again. Some people never start dating again, they simply cannot move through it. I worked with a woman who was a relatively young widow who had lost her husband about six years previous. She wore her wedding rings (and his) and when asked out
would tell people she was married. Little strange? IMO yes...but she was happy with it. (And she had been in counseling as well...she simply did not want to date, she had a bunch of kids and had decided not to even think about it 'til they were older).
Some people simply don't do well alone, AND are fantastic people. We've all known of someone who was married 20-50 years, loses their spouse (and it was a love of their life, wonderful marriage situation) and is remarried less than a year later. But people don't generally bitch about this because everyone was concerned if the one spouse was gonna follow the other, and EVERYONE knows how much they loved each other...so people are usually glad.
So, ultimately...it depends on the person. Maybe it is too soon for her, but it's not your place to say so. As long as they are happy, aren't doing anything extremely unhealthy (such as being romanced by a con artist) ...it's simply not your business.
IMO, you're not done mourning (clearly). And it may take you a lot longer because the grief you're experiencing isn't all consuming as it can be for a spouse. You're mourning differently, especially if this person was involved in raising you. Understand that she is still mourning too, and just because she's seeing other men, she's not being disloyal to Jon. Jon is dead, and in all likelyhood assuming he was a nice guy...would want her to be happy.
You should be glad she's doing well and not coming to live with you.
As far as 'uncles' go...you're an adult. They're not your 'uncles'. You have no obligation to interact with them any more than you'd interact with someone a relative was dating. You'll like some, and hate others. But it's all about whether or not
she is happy.