>is there any views on what would be acceptable for me to ask?.<

Sanjay, I'm sure no one on this forum, would want you to refrain from ask any questions here - . However, I'm not sure that anyone but you can decide about questioning Rawat - that is whether you should risk alienating your family by treating Rawat with seeming disrespect - and just what kind of questions you need an answers to. 

Of course you have now revealed your identity - and I hope this isn't too much of a concern but you should know that Elan Vital monitor's the exchanges here - if your step father has the involvement you say he does then I suspect your contribution will get reported to him and perhaps your mother. In the light of that, before you go any further with ideas about challenging Prem Rawat I strongly suggest that  you consider trying to discuss how you feel about this with those members of your family to who you are closest.

The behaviour of the premies that you describe is horrible and I'm sure you must feel very angry toward them for their insensitivity - however try not to let that spoil the time you and your dad had together. Seems like he was way closer to you than he was to his Guru - the fully paid up premies simply can't understand that, so again my advice is not to make it an issue with your relatives - it's probably a no win situation.

Goodluck whatever you choose.

Nik