Im currently in this situation - 3 older boys close together then a 4y2w age gap to the baby.

Bub is 10wks old so we're still in the early stages of this dynamic and Ive had the same concerns as you re: closeness with the age gap. Our three older boys are quite close and I worry that bub will miss out on the relationship of having a sibling close in age to hang with. They adore him and cant wait for him to be mobile so they can entertain him but Im sure there will be times where the novelty of a younger sibling wears thin. We are raising them to remember how important your siblings are and encourage the close bond we want them to have. My biggest worry is next year when bub is a year old and all the other boys are at school - will he be lonely? When he is older and wants to hang out with them but they're off doing teenage stuff - will he resent it?

In the end, it is what it is and people who've been there have assured me it works out just fine.