Wedding Processional

Assuming your dad is walking with you...I would say your mom, his parents (walk together or separate depending on what they are comfortable with), grandparents, MOH and BM together, ring bearer with/followed by flower girl, then you and dad.

Wait a lot of catholic churches don't allow non catholics get married in their church.

This is false. Most Catholic churches, if not all, allow for a marriage between a Catholic and non-Catholic to take place. It's just that a full sacramental mass is usually not performed (but a ceremony is still permitted). I know this because I'm a Catholic marrying a non-Catholic.

Mmm, no my sister in law and brother in law will not be getting married in a catholic church due to him not being catholic.

This still sounds incorrect. Catholics always have the option of not getting married in a Catholic church, which sounds like what your in-laws are doing (and is totally fine). But officially, a marriage between a Catholic and non-Catholic is very much permitted, provided they get permission from their parish/diocese:

http://www.catholicweddinghelp.com/questions/wedding-form-options.htm

Another Catholic here.... marrying a non-baptized, non-Catholic within the sacred doors of a Catholic Church lol. Of course it's allowed! As to the original question.... ugh, good luck! Our wedding is coming up this Fall and I'm still trying to navigate things. What has me most stressed are selecting the processional/recessional "songs". There are like 3 to choose from, lol. Good luck!

A Catholic can marry a non-Catholic in the Catholic church, although they do need to get permission:

https://www.foryourmarriage.org/catholic-marriage-faqs/

The Catholic partner will need to promise to do their best to baptize the children and raise them as Catholics. The non-Catholic partner doesn't need to promise anything, except for the marriage vows.

I am saying their church was not allowing them to do it.