My Know all Brother

I'm Nigel 27 just finished university and got a job with my brother Donald 31 the oldest of 3 and I'm the youngest. Donald started his own company and has done very well for himself and with his trust fund providing the money for his company until started paying for itself. He is and has always been a know all. He married Jenifer 29 while he was at university and plays up on her regularly. Jenifer has given him 2 children 5 and 3 and Donald hasn't bothered much with her since the arrival of the last child. He goes out of town every chance he gets and sleeps with women he meets. I'm the polar opposite to Donald always felt awkward around women, but feel comfortable around Jenifer. It's me she calls when she need help and Donald is away, I've dated and don't do too badly at times, but strike out a lot more than I score. I like fishing and to that end I bought a island on a lake it had a house already on it and after some work it has become my getaway spot. My parents and extended family also use it. But Donald doesn't it's too boring for him. I took a break and went to my island to fish and relax by myself. Donald was going away on another business trip and Jenifer wanted to join him and wanted to bring the children along as well. Donald didn't want them to tag along and it was he who suggested Jenifer and the children goes to my island and have a holiday there. I would be there he told Jenifer to help an eye on the children. Donald rang me and asked if I would mind, but not leaving me much chance to refuse either. Our parent also came for the first 2 days and then returned home for their country club dinner. That left just me and Jenifer and the children on the island over following days we had great fun altogether and then late one night with the children in there bed asleep, I was going to shower than bed. Jenifer asked me would I mind her joining me in the shower. I was a little shocked at her request at first, but nodded okay. We showered together and then slept together, fucking twice and again in the morning and continued even after we had returned home. I get regular sex from Jenifer, she reckons if Donald can fuck any woman he wants she can fuck me as really likes me and knows I won't betray her like Donald. She has started trying to get me to linkup with a girlfriend of hers Emily 27 and both Jenifer and Emily have slept together before and Jenifer thinks we would good for each other and she would still get to join in with us as well. I've only slept with Emily in a threesome with Jenifer so far and am open to having a relationship with her and would consider possible marriage as well. But one step as a time, Donald is still unaware of Jenifer also having a fling.