Practice Certificate(s)?

Me and a friend are considering starting our own practice but are becoming slightly confused on the issue of obtaining  practice certificates from our professional bodies.

I am AAT qualified and my soon-to-be partner is part ACCA qualified. I am aware that I should obtain a practice certificate from AAT but am aware that this will prevent me from joining another professional body (ACA or ACCA for example) as I am already in practice. I am slightly disappointed to find that joining the AAT MIP scheme will prevent me from gaining any further professional qualifications, or is there any way around this?

My soon-to-be partner is part ACCA qualified so surely she won't be allowed a practicing certificate from ACCA?

Would it be OK for us to both trade under my AAT practicing certificate until my partner finishes her ACCA? Then could we swap and both trade under her ACCA certificate whilst I join another accounting body to study towards ACA/ACCA?

Any help would be greatly appreciated!