Player joining the party last gets dropped during finding game or right after it

Hello Good People of EA NFS Unbound Team, 

I would like to thank you for bringing this superb thing to us, its amazing beyond wildest dreams. (I love nfs). Also huge bundle of thanks for the Vol. 6 Updates, its really delightful to see that the game will be improved/updated regularly. 

I bought Unbound back then myself and after the The Grand i was kinda less motivated to play offline so to play multiplayer ive bought 2 additional copies for my siblings. We really like competing each other and its fun. 

However there is one big problem we have been facing on and off in Unbound. I usually start the game and create a party and send invite to both siblings. Both of them accept in any order, and once they do i start the game "Find a game", during this finding game server the sibling who accepted the invite last will be dropped from party. I'll ask the connected sibling to "Leave game" and i myself would also "Leave game" and create party and send invites again. Again the sibling who accepted invite last, will be dropped either during finding servers or sometime after the game has started and we are in 3d world. When this happens we know that the day is lost, and we all have to quit Unbound and play some other game. Which we also play online, multiplayer and it works fine i.e. no connection drop issues. On some lucky days we dont find the aforementioned problem and are able to play to our hearts delight, on some days this starts happening after few races. But once a sibling is dropped during connection to servers we know that we aren't going to be able to play it today, no matter what you do. 

Sometime when it doens't happen immediately after we started our game session and instead happens after 1-2 hours of gameplay, when we create party again and join i noticed that players connected to server are 1-2 which has led me to conclude that other players were dropped too and they are also re-joining.

I've followed the existance network troubleshooting guides to no avail, let me share more info which might be helpful.

Two siblings have 16gb ram + gtx 4070, one sibling has 32gb + gtx 3070, these are combined with very good processors and other gigs.

We have 30mb fiber optic internet connection. We are in same house, so same connection is shared between three pcs. When we are gaming there is no other heavy usage of internet going on. 

Also the peculiar fact  that whoever accepts the invite last will be dropped. Also after this happens we are able to join separate servers and play separately but we want to play in same party same server. 

Please let me know what we can do to resolve above issue. It really ruins the mood when you are all excited to race and suddenly you realize naa aaa, the EA servers says thou shall not pass. :-(