ok, i kinda "get" the sharing a month thing - it can be painful if you have people that need to travel to ask them to travel twice - makes sense - we planned DD's baptism for the same weekend as my mum's 50th so that people only had to travel once. however, if you don't want to organise your childs baptism to coincide with the month of someone elses, it's up to YOU to change your plans. your DF's cousin has every right to plan the baptism of their child whenever they want. it's not like you said "ok, my baby is due then, we're having baptism on x date" and then the cousin organised it for x date. they are planning the baptism of their child at a time they are happy with, and you need to do the same for your child.

i guess you need to step back and decide what is important to you. if you want a small intimate thing, HAVE a small intimate thing. you don't have to go all out! if the other baptism "overshadows" your childs, does it matter? a baptism isn't about the pomp and ceremony, it's about introducing your child to the church and starting their relationship with God. the party afterwards isn't about that. the party afterwards is about celebrating your child with the extended family/community. how you choose to celebrate that is entirely up to you.

i would suggest you find out when the baptism is and plan your own childs around that. you have NO plans in place at this stage, they do - it's up to you to work around them