See every gemstone is dangerous in the sense if you wont follow the lifestyle desired by the particular planet, then after wearing gemstone of that particular planet will give out some negative results to you. And if you were wearing an unproperly engerised gemstone than it will loose its astro power, then it will become the ordinary stone thats it. Ya there are few people / astrologers who glorify the effects of gemstone in each one’s life, Yes i do agree it has some effect, that too if you follow the strict rules desired by the planets / nature. You can’t go against the nature, if you go then only you start facing the problems.
So if you have decided to wear neelam and get benefits then you need to sacrifice some of your habits which are restricted if you wear blue sapphire. So its like if you want some thing you need to loose some thing.
Alternative to emerald, semi precious stone what i would recommend is green tourmaline usually cobachon type.
Yes you have lagnat, shukrat mangal dosh which i can say 60%. And more than mangalik you are having Rahu and ketu dosh, which will interfere and trouble your married life.And if still not married it will create breakups in the marriage due to doubtfull nature among the couples.