you might not like the things im going to say, but please read it anyway. im a 'to the point' kind of girl... so bear with me.
ok, first of all, this isnt all about you, this is about your family. sure, this seems like a good option, but your husband is unsure and concerned, and that should be a GOOD thing to you. im not saying that he doesnt trust your mom, or that there isnt a reason to trust her, but your husband is your husband! im sorry, but HE AND YOU have to make this decision. im not at all seeing that you are stuck between grandma and hubby, i see and hear disrespect toward your husbands feelings and concerns, and you putting your and your mother's ideas and needs against your husband. its like you are taking sides, and you should be taking the side of your partner that you promised to love until death! even if you dont agree, your husband has concerns, and that should be respected.
what you NEED to do is to sit and talk to your husband, away from kids and other responsibilities. ive found that guys talk well when they are driving :P talk to him - find out what he feels. dont pressure him to go along with your plan, you may find that talking it out respectfully and consideratly might have him on board without even saying a word to force him! talk to him! find out his concerns! write them down. perhaps then the both of you talk with your mother as well if he has specific concerns that involve her. get his concerns and questions answered.
heres the other thing that you should be grateful for; your husband wants your daughter around! he doesnt want to be separated from his daughter for such a long time! hes obviously connected to your daughter in a complete and loving and wonderful way!! why mess with THAT!?! kids at all ages need their parents, but when they are younger they NEED their parents !!! its not going to be a very good idea to 'get rid' of your daughter for such a long time, at least not in my mind. im a child care provider, so i do have the developmental training to say that. if it were for the weekend, or just a few days, that would be different. but for a month-ish? come on ! dont you want your daughter around?!?! im sure that the time spent with your daughter, especially for your husband, is worth more than the money you might have to spend on child care. you have a 14 year old, cant the 14 year old care for the 3 year old? i was taking care of my little brother when he was 1 and i was 12, and i did great. sure, i dont know your oldest, maybe she is not mature or responsible enough, but give her a chance, perhaps let her watch the 3 year old when you are around, but busy, see how she handles taking care of a kid. older children are usually able to deal with siblings just naturally.... i dunno. :P ive seen a lot of siblings, and no matter if they are 7 months apart (for real!!) or 11 years apart, older always take care of the younger in one way or the other. so give your oldest a chance! perhaps pay her - even if its just a dollar an hour - or if its a special purchase or trip or privelege. perhaps, for every hour of babysitting she can earn an hour of friend time on the weekends or something. you CAN work this out.
but most importantly, you need to respect your husband!!!
i would HIGHLY recommend purchasing a book called "the proper care and feeding of husbands". its fantastic, and you are not the only woman to have troubles like this with her husband. what we women have to realize is that we have WONDERFUL, deserving, willing, and dedicated husbands, but the way WE treat THEM is appalling. im guilty of it myself, but since reading that book, my attitude, and my whole marriage, has changed for the better!!! ;D its all on your outlook! instead of thinking "my husband doesnt want our daughter to have this experience, he doesnt want to do this the way i want us to" you should be thinking "my adorable husband will miss our daughter TOO MUCH to send her away for that long!" - and that, my dear, is rare and BEAUTIFUL!!!! :D :D :D :D :D !!!!