First of all, I was the person who edited your original message. If I have misinterpreted anything you said, let me apologise right now.
The problem is, as editors we are expected to proof read the messages sent in to us, and modify them to make them correct as far as English language is concerned. While I could understand what you are saying, some of it needed careful interpretation.
Now let's look at your situation. I would say that your sister-in-law is either a lesbian, or she is bisexual. The fact that you enjoyed her touches and caresses would suggest that you also have at least some bisexual tendencies. This is not surprising, as those who are experts in this field of human sexuality estimate that one woman in three, worldwide, has at least some bisexual component to their sexuality, and one woman in seven is a lesbian. If your sister-in-law likes guys as well as girls, makes her bisexual.
I'm not interested in making moral pronouncements, nor am I going to judge you as to whether what you are doing is right or wrong. Each of us has to make those decisions for ourselves, and come to terms with what we feel is acceptable, and what isn't.
If you wish to enjoy a bit of extra excitement in your life, that is up to you. Personally, I don't see why you have to decide between doing one thing or the other. If both activities bring you pleasure, then why not enjoy both of them? You get to see your sister-in-law on a regular basis, and it gives you ample opportunities to explore sex with another girl. You also allow your uncle to touch your breasts, and so far you haven't allowed him to go any further than this. Neither of the activities you are involved in has made you love your husband any less, and neither of the activities you are involved in are doing you any harm.
I am happily bisexual, and I have been ever since I was a little girl. I have always known I liked other girls as well as boys, and some of my earliest sexual experiences were with other girls. I have always loved sex with both girls and guys, sometimes both of them at the same time. If you enjoy touching your sister-in-law, and her touching you, there's no harm in it, and it can be very fulfilling and beautiful experience, quite separate from making love with your husband, or falling around with your uncle. There can be a tenderness between two women that cannot be matched by any other kind of sexual relationship. Everything that you have said in your post suggests that you already feel the excitement when she touches you, and when you touch her, I'm sure that the excitement just increases.
Many girls fantasise about an older man, and with you, this manifests itself with your uncle. He's an older man, and there is the added illicit thrill of an incestuous liaison. If you chose to let things go further, it wouldn't surprise me. Sexual excitement has a habit of letting things get a little bit wild and out of control, and as your uncle is already trying to place further demands on you, you have to consider how long it would be before you gave in to your own excitement and desires. If you can keep some sensible boundaries around this, then there is no risk to your marriage. But you have two be very careful. In either situation, with your uncle, or your sister-in-law, you are playing with fire, and if you play with fire, there's always the risk of getting burnt!!!
Many men find lesbian sex extremely exciting, and perhaps your husband would be extremely aroused if you are having sex with his little sister. Have you ever talked about lesbian sex with him? And if so, what was his reaction? You could try jokingly telling him that you think his little sister is really cute, and see how he reacts. Who knows what he might suggest? Perhaps he already knows that his little sister likes you in that way, and he may even encourage it.If he wanted to join in, how would you feel about it?
The feelings you are experiencing with your sister-in-law may seem really strange to you, even as they excite you. If you want to talk to me about these things, by all means get in touch through the PM system. As I say, I am bisexual, and I understand the excitement that having sex with another girl can generate.
So, as far as I'm concerned, you don't really have to make a choice of either or, rather, you have to decide if you want to go ahead with your extra marital activities, and if so, how to conduct them discreetly.