Thinking of having a joint bday celebration with dp but want to invite all our friends on a lovely boat which

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is a dinner, dance,also want to tell them all that my surname has changed to dp surname though not through marriage,wanted them all to celebrate our bdays and my new surname,we have been together a long time so this means alot to us both.however
It would be £30.00 per head and we will pay for drinks for a little toast for surname, and birthday,is this being unresonable for them to pay to come.

Is this something that you do as a group anyway - hire a venue and have a party splitting the cost ? If not I'd be pretty peeved to realise I am funding what is effectively your party.