If 2 Catholics, both baptized Catholics, live together first before marrying (not as brother & sister) and there is no confession - at least by the husband - before the marriage vows take place, is that marriage valid?
Would it have any effect on an annulment decision? They ask this question in the forms.
Uncertain. It might help them discern other factors like maturity. Basically, they need as complete a picture as possible of the lives of the spouses at the time of marriage. That is the only way the tribunal can render an accurate decision.
The sin of a sacrilegious communion does not impair the validity of the marriage. There must not be any impediments, such as duress and lack of free consent to enter into the marriage. If they were married by a priest before two witnesses, it is valid.
In speaking about forms, I presume you mean annulment forms? It could reveal the lack of maturity to enter into the sacrament, perhaps, demonstrating a very lax conscience. The tribunal would need to review the particulars all the way back to dating and engagement.
If both parties want the annulment, does that have any bearing?
No, not really. An anullment is only granted if the tribunal discerns that an impediment to marriage existed at the time of the wedding. The fact that both people now want a way out doesn’t really have anything to do with whether or not there were any impediments at the times of marriage.