L.N.
I nursed three childen. Each one is different, but like Sandy says the best thing to do is follow the babies lead. 2 weeks is still very early and you are still establishing your supply. If you supplement with formula now you will interfere with the supply and demand. As long as your baby is having 4-6 wet diapers a day and is gaining weight then your milk should be enough.
Tell your family that it is very important to you to nurse this child and, even if it was ok for them to "just give the baby a bottle" that isn't what you want to do and that what you really need from them is for them to support you in what you feel is important to you, in this case not to undermine your breast feeding of this child. Breast milk is what nature intends for babies to be fed. Formula is fine, but it is only a subsitute for the best food for a baby. Scientists are always discovering some new substance or nutrient that is in breast milk that formula doesn't have. Why not give your child the best?
As far as nursing with an older child, I would get a little "feeding station" going on the chouch. Get a glass of water for yourself, have your son get some of his favorite toys and books nearby and when it is time to nurse have him come and sit by your side and you can read a book to him while you sit with baby. You can enlist his help turning the pages of the book and it can be your special time together. You can build him up by emphasizing how big he is and what a good big brother he is, he can get diapers for you and other little helping things.
You can have him play nearby,maybe work on puzzels, color etc. If he is bored with baby and you always nursing baby, you can tell him when he was little you nursed him like this also and look how big he has grown and his baby sister will grow bigger also. You can also have a bunch of videos and when it is nursing time he can settle down to watch a video with you. On nice days you can sit outside with him and let him play nearby. You can use a blanket over babies head to cover up if you feel you need to.
There is a poem that I recall that goes "Cleaning and scrubbing can wait
settle down cobwebs, dust go to sleep. I'm NURSING my baby, and babies don't keep!" In other words this will be a very short time where your baby is so "needy" and as someone once told me "this too shall pass" when I complained about the neverending needs of my baby.