HI
manuelaux. The guidance for Marriage Visitor applicants is here:
http://www.ukvisas.gov.uk/en/howtoapply ... rs#9248746
It's not very extensive. Basically I think your main concerns are to provide evidence that you are planning to enter a CP during the 6-months your visas will be valid, and to show that you are then going to leave the UK. Remember you have to satisfy the general requirements for visitors.
Suggested evidence:
Details of the Register Office where you have made enquiries, and printouts of any correspondence, information etc. you have gathered should be supplied. I do not know how far you can go with bookings, notices etc. before you actually arrive: check with the Register Office and get as far as you can.
Details of any ongoing commitments in Croatia should show you intend to leave: jobs, tenancy agreements, family ties etc.
Evidence that you can fund yourselves (i.e. you won't claim any public funds and won't be trying to find work).
Details of any accommodation you have arranged in advance.
A return ticket, or the funds to pay for one.
I know
Wanderer did mention in your other thread that he thought there was some kind of proof-of-relationship requirement for proposed civil partners. I have to say I can't see it anywhere in those terms (apart from the much more specific requirement to show you are planning to enter a CP), but he may come in and let us know!