How to decline an offer already accepted - new offer is better

Dear sir,
I received an offer letter from two reputed firm.
First I accepted the offer from xxx company.
Later on I received an offer from yyy company.
I like to join yyy company.
Will there be any problem for me & my family. if I am not joining them.
They have done home /certificate verification.
I still didnt join any of these firm.
please advice.

If you first accepted offer of XXX company and now do not want to join.Inform them in writing.
Did you report to their office and formally join work there?
If that is not done then there is not much of legal hassle.

dear sir,
I didnt join any of these companies.
Received offer letter from xxx company and accepted their offer.
I have not informed them and if i inform the xxx company will they do any trouble to me & my family sir.

No sir I didnt join formally at their office.
Through mail only I gave my acceptance.

Dear R shriram,
You need not worry much and you can simply reply on email to Xxx company for not joining them. There will be no legal Hassel for you as you are not an employee of that organisation.

Dear Friend,
There is no issue if you have not jouined. You inform the XXX firm give out a personal reason for not joining. Simulteneously report for joining in YYY firm soon of your choice to avoid unprecedent situation.

Hi there,
It is good, you have not joined the new company. So, you can write back to them saying that either due to personal reasons or better prospects, you are not able to join them.
It is courtesy from side to inform the 1st company, so they can roll the offer to next candidate in line, rather than keeping them in dark.
How will the other company know, where you are joining and how they give you any trouble is not understood though.
But remember one thing, don't keep salary alone as a criteria to join a company. Every company has its share of politics and problems.
If your Habitual job hopper, just by seeing one's resume it will be known. This also can form a basis to reject in a new company, even if you have done well.
Best wishes.

thank you mr.prabhat ranjan mohanty , mr. Manoj Kamble , mr.ssrow ....you all cleared my doubt.
And In fact i am not focussed on salary sir. Two companies are paying same salary only.
But I Like to join yyy.
Peace of mind will be better than xxx company than pressure of mind for same salary.
thatsy.
thank you for everyone who gave hands when i was in question.

Whatever the reason, for joining or not joining one of the two, be absolutely honest about informing the one, why you have decided not to be a part of their team.
This will save you a lot of unnecessary headaches later on, and you will reflect that you possess and integrity and honesty, among other things, as positive traits.
For some young and curious minds taking on to jobs for the first time, or for switching jobs later on, remember to see does your passion equate with the skill you need to carry on your job, the growth potential in the long term, and that you are at home with the work environment and culture.

Dear arih ur rehman sir,
Yes I will Surely inform the xxx company anyway.
What I want to know is whether there will be any problem for me If I inform them honestly.