just a quickie..

[HowAnnoying]

Is it

to celebrate Jo and Johns Baptism
to celebrate Jo and John's Baptism
to celebrate Jo and Johns' Baptism

and should it be baptisms??

How about "The baptism of Jo and John"? But if not it should be "to celebrate Jo and John's Baptism", though this opens you up to the possibility that you mean to celebrate Jo, and also celebrate John's baptism. Baptism is an abstract noun as well as an event, so sounds odd when turned into a plural, hence your reluctance to say "baptisms" and my alternative suggestion.

Yes I wanted to write "the baptism of Jo and John" but it wouldn't fit!

Thanks for your help.