Currently your toe as executor is to fresh with legal requirements of the will ,( dint worry that you have to rush in frantic time, it's accepted that people grieve, have lived, and there can be a lot to do) and then to distribute anything l thing obtained from the deceased property, money chaos, the family pets even) in avoidable with the explicit instructions if the will.
As a matter of interest and legal possibility if it is something YOU are interested in at she point and may get is reasonable after extensive consideration and possibly construction ( which in this case may well be advisable), note tha a will can be changed up to 2 years after the date of the death in a deed if variation which is a very simple legal document for a solicitor to construct v and will l should take less than an hour. Importantly this applies only to anyone who is being deprived of assets they would have inherited who needs to further agree to this in t writing in he variation which a legal document which essentially becomes a new supplementary version of the will sharing that you gl deduct some of your inheritance in whatever firm and give it to other beneficiaries ( normally those already mashed by increasing what they already were gifted, or in some cases adding in a further family member child who had subsequently been both after the will was written but another one had not been completed in time to update the information- everyone mentioned in the will would be affected by verification and have to shed to this ,NB.). For records and proof you should get variations signed and witnessed by a solicitor. Probate needs to be completed and applied for in the standard way and nothing can be proceed ef further until it is granted and the stairs private firm is switch and received.
really Importantly @user1471461828 ,on this issue you should feel under absolutely no pressure or coercion at all to do this and you are under no obligation whatsoever to make any amendments. I think the other the other beneficiaries would struggle to successfully challenge you In this case. You are the biological child of the deceased wheras they are not as I understand it so I believe it would be seen as reasonable you would be gifted a greater proportion. I presume they're is no way they could be obstreperous and attempt to claim dimished capacity on the party if your father at the time the will was made. I have known this to happen( it wasn't the case but caused an almighty, spiteful, and unnecessary headache, prior can become horrible and greedy dinnertime over not l been large sums of money, and I think that's when they show what their make of. It's just do sad).. as an additional point for consideration did your father have any of your step siblings living with him or provide ongoing financial support for them which he didn't for you for some reason? If they had been thst position, they could possible now try claiming to be at s great disadvantage financially without this and require more money? That might be the only possible ground for a challenge, however there would have to be extensive provable evidence on all fronts and with an inheritance providing s financial fun I do don't how successful they would be anyway I'm going to assume this isn't the case for now anyway.
You appear to be In s position where your slightly bigger proportion sounds reasonable ,I don't know the history of familial relations etc ,(were you brought up from birth as siblings full time, brrought up from years apart only seeing your step siblings occasionally- maybe the even moved to the far end of the country... There are multiple unknown s( they then may have only been seeing their father rarely too in one potential scenario).
Your Step sibs may be disgruntled, ,but your late father's wish a clearly expressed in a legally accepted format. How well you get on with them and how you wish you relationship to continue may affect whether you need to pursue a variation it are hair to stick with the status quo c and let things lie. These are all things they can't make you do. only pursue making a variation if you are sure you want to take that route , are very sure, and get guidance from a professional with experience in exactly this. Not all solicitor actually have experience in variations even if they are solicitor who deals with wills and estates
However meanwhile, Wait.... see how things go, let the shock and grief subside a little and see how your relationship goes then decide how you want to proceed. You have up to two years to make and submit the changes.i hope it works out, you aren't harangued and your life is taken over. To me personality, this would be reason if enough to day no as I hate this if sags. If but the,,m something really decent and meaningful , but wouldnt participate in the game. Hopefully you won't get involved in such a game and are left practically alone to live your life happily ,