You are using SPSS and I only work with Stata, so I cannot give you SPSS code. In Stata correct steps would be as follows. You want to merge on the household id code, which is whhid in the WI file and is the first 12 characters of caseid in the IR file. I hope than in SPSS you know a way to extract the first 12 characters of caseid.

use e:\DHS\DHS_data\WR_files\PKWR21FL.dta, clear
sort whhid
save e:\DHS\DHS_data\scratch\PKWRtemp.dta, replace

use e:\DHS\DHS_data\IR_files\PKIR21FL.dta, clear
gen whhid=substr(caseid,1,12)
sort whhid
merge whhid using e:\DHS\DHS_data\scratch\PKWRtemp.dta
tab _merge
keep if _merge==3
drop _merge