Re: If you have trained in both Aikikai and Iwama, please help me...
Go on and try it. Whether doing two styles at the time works or not probably largely depends on the people involved.
I have travelled through a couple of different Aikikai flavours, and also spent a summer - not more - in an Iwama dojo. I brought "home" with me two important things: first, preciseness and details in bokken work. Although I did not like all in the Iwama teachers way of dealing with bokken, it was great to always be given time for suburi before going into partnered work. Second, preciseness in hanmi. I did my first aikido term in Nishio type of aikido, where they do not stand in normal hanmi but their feet is more like in kendo or iaido. When I transferred to this other Aikikai dojo, noone seemed to care much about the details in where I put my feet - byt the Iwama teacher did. Coming back to my Aikikai dojo, I realised that a couple of the people whose aikido I thought highly of had a very similar hanmi leading to very similar foot positions in some conditions. Getting my feet on that line really made a difference for my aikido.
It was difficult to come back, though. The main teacher of my "home" dojo did not look too mildy on my "iwama-isms" - he never said much about it, only a couple of things at a couple of occasions, but I knew I had been "unfaithful". The experience of another place also made me look at some things in the dojo with more critical eyes. In the end, I travelled further to the Endo sensei line of aikido where uke should follow and make sure to stand in a good position rather than resist. It is a completely other set of pedagogics than Iwama. In a way these two types of aikido build skills in different ways, you eat the cake from opposite sides.
During my time in the Endo type of aikido I also worked continously with a teacher who worked with resistance as a method, as Iwama style and many other lines of aikido do. I felt it good to combine these two approaches - but I much prefer to have them separate. I believe in both these ways as valid, but have difficulties in believing in the "inbetween" ways where people resist a little bit like they feel like, and have no real system for how and when they should resist.
This was probably not the kind of answer you asked for... but it is mine.