If you keep connecting them their friendship will eventually reach the 4 hearts level which means they are in love and if you connect them some more they will have a baby.
I know this is kinda out of the way but I tried connecting my tamagothi with another and it did nt go through how exactly am I supposed to connect with another tama. Also I read the Q&A and it said that to much sunlight would be a downfall but I was inside so that was not the problem.
Just make sure that the same option is being selected on both tamas (present, game or visit) and also make sure that they are a few inches apart. Keep trying! It'll work!