That is certainly the ddl. Unfortunately that is for only one table. The other challenge is there are lots of errors when I try to load this on my local instance.

Msg 1767, Level 16, State 0, Line 2

Foreign key 'FK_ProposalProfitSplitWorksheet_db_branches' references invalid table 'dbo.db_branches'.

Msg 1750, Level 16, State 0, Line 2

Could not create constraint. See previous errors.

Msg 4917, Level 16, State 0, Line 2

Constraint 'FK_ProposalProfitSplitWorksheet_db_branches' does not exist.

Msg 4916, Level 16, State 0, Line 2

Could not enable or disable the constraint. See previous errors.

Msg 1767, Level 16, State 0, Line 2

Foreign key 'FK_ProposalProfitSplitWorksheet_logins_AcceptedByInstallingBranchImpersonatingUserID' references invalid table 'dbo.logins'.

Msg 1750, Level 16, State 0, Line 2

Could not create constraint. See previous errors.

Msg 4917, Level 16, State 0, Line 2

Constraint 'FK_ProposalProfitSplitWorksheet_logins_AcceptedByInstallingBranchImpersonatingUserID' does not exist.

Msg 4916, Level 16, State 0, Line 2

Could not enable or disable the constraint. See previous errors.

Msg 1767, Level 16, State 0, Line 2

Foreign key 'FK_ProposalProfitSplitWorksheet_logins_AcceptedByInstallingBranchUserID' references invalid table 'dbo.logins'.

Msg 1750, Level 16, State 0, Line 2

Could not create constraint. See previous errors.

Msg 4917, Level 16, State 0, Line 2

Constraint 'FK_ProposalProfitSplitWorksheet_logins_AcceptedByInstallingBranchUserID' does not exist.

Msg 4916, Level 16, State 0, Line 2

Could not enable or disable the constraint. See previous errors.

Msg 1767, Level 16, State 0, Line 2

Foreign key 'FK_ProposalProfitSplitWorksheet_logins_AcceptedBySellingBranchImpersonatingUserID' references invalid table 'dbo.logins'.

Msg 1750, Level 16, State 0, Line 2

Could not create constraint. See previous errors.

Msg 4917, Level 16, State 0, Line 2

Constraint 'FK_ProposalProfitSplitWorksheet_logins_AcceptedBySellingBranchImpersonatingUserID' does not exist.

Msg 4916, Level 16, State 0, Line 2

Could not enable or disable the constraint. See previous errors.

Msg 1767, Level 16, State 0, Line 2

Foreign key 'FK_ProposalProfitSplitWorksheet_logins_AcceptedBySellingBranchUserID' references invalid table 'dbo.logins'.

Msg 1750, Level 16, State 0, Line 2

Could not create constraint. See previous errors.

Msg 4917, Level 16, State 0, Line 2

Constraint 'FK_ProposalProfitSplitWorksheet_logins_AcceptedBySellingBranchUserID' does not exist.

Msg 4916, Level 16, State 0, Line 2

Could not enable or disable the constraint. See previous errors.

Msg 1767, Level 16, State 0, Line 2

Foreign key 'FK_ProposalProfitSplitWorksheet_logins_CreatedByImpersonatingUserID' references invalid table 'dbo.logins'.

Msg 1750, Level 16, State 0, Line 2

Could not create constraint. See previous errors.

Msg 4917, Level 16, State 0, Line 2

Constraint 'FK_ProposalProfitSplitWorksheet_logins_CreatedByImpersonatingUserID' does not exist.

Msg 4916, Level 16, State 0, Line 2

Could not enable or disable the constraint. See previous errors.

Msg 1767, Level 16, State 0, Line 2

Foreign key 'FK_ProposalProfitSplitWorksheet_logins_CreatedByUserID' references invalid table 'dbo.logins'.

Msg 1750, Level 16, State 0, Line 2

Could not create constraint. See previous errors.

Msg 4917, Level 16, State 0, Line 2

Constraint 'FK_ProposalProfitSplitWorksheet_logins_CreatedByUserID' does not exist.

Msg 4916, Level 16, State 0, Line 2

Could not enable or disable the constraint. See previous errors.

Msg 1767, Level 16, State 0, Line 2

Foreign key 'FK_ProposalProfitSplitWorksheet_proposals' references invalid table 'dbo.proposals'.

Msg 1750, Level 16, State 0, Line 2

Could not create constraint. See previous errors.

Msg 4917, Level 16, State 0, Line 2

Constraint 'FK_ProposalProfitSplitWorksheet_proposals' does not exist.

Msg 4916, Level 16, State 0, Line 2

Could not enable or disable the constraint. See previous errors.

Obviously you have a little work on the ddl before we can get much going here. Why does your boss ask for this to be done in a trigger? What they are asking for is referential integrity and triggers are not a good choice for that. One issue is you will likely have to write at least 2 triggers for this. An update and an insert. The reason triggers are not good at enforcing RI is because they can be disabled. Let's say I want to force a row in that does not meet the criteria. I simply disable the trigger, insert my data and then enable the trigger.